learning resource material on irrigation engineering

LEARNING RESOURCE MATERIAL

ON

IRRIGATION ENGINEERING

(CET403)

UNDER EDUSAT PROGRAMME

SCTE&VT, BHUBANESWAR

ODISHA

Coordinator: Sri B. C. Sahu ,

Sr. Lecturer (Civil)

Govt. Polytechnic, Nabarangpur

Nodal Officer: Dr. P. K. Muduli,

Sr. Lecturer (Civil).

Govt. Polytechnic, Kendrapara

1

CONTENTS

Chapter

No.

Topic Name Page

No.

Prepared by

01 INTRODUCTION 2-6

Ms Amrapalli Sahoo,

Lecturer (Civil),

JES, Jarsuguda

02

HYDROLOGY

7-16

Sri Satyananda Sethi

Lecturer (Civil),

GP, Sambalpur

03

WATER REQUIREMENT OF CROPS 17-22

Smt. Sailaja Bhuyan,

Lecturer (Civil)

UGIE, Rourkela

04

FLOW IRRIGATION 23-32

Smt. Sailaja Bhuyan,

Lecturer (Civil)

UGIE, Rourkela

05

WATER LOGGING AND DRAINAGE

33-36

Sri D. K. Mohapatra

Lecturer (Civil)

ITT, Choudwar

06

DIVERSION HEAD WORKS AND

REGULATORY STRUCTURES

37-46

Sri Sudhakar Naik,

Lecturer (Civil)

GP, Gajapati

07

CROSS DRAINAGE WORKS

47-54

Sri Sanjeeb Meher

Lecturer (Civil)

GP, Sambalpur

08

DAMS

55-70

Sri D. Kura

Senior Lecturer (Civil)

JES, Jharsuguda

09

GROUND WATER HYDROLOGY 71-94

Dr. P. K. Mohanty

Principal,

ITI, Dhenkanal

2

CHAPTER -1

INTRODUCTION

Irrigation Practice in India can be traced to prehistoric times. Perhaps the earliest reference

to irrigation is given by the great sage, Narada who come to see the Emperor, Yudhishthhira, around

3150 B.C and asked “Are the farmers sturdy and prosperous? Ancient Hindu rulers took very keen

interest in construction of irrigation works. The account left by Megasthenese – the Greek

Ambassador of Sleukos Nikator to the court of Chandra Gupta Maurya also gives some idea about

irrigation in India around 300 B.C.

The Muslim rulers also took keen interest in constructing canals for irrigation. In the 14th

Century, Sultan Firoz Tughlaq constructed a number of canals from Sutlej and Yamuna rivers. Akbar

remodelled Firozshah canal in 16th

century and put it in use again. State controlled irrigation works

have begun to play a major role only in the last about 150-200 years. In the 19th

Century , the British

Raj was more concerned with the improvement of existing irrigation works than with building new

ones. Three important irrigation works – Western Yamuna Canal, Eastern Yamuna Canal and Cauvery

Delta System were remodelled and opened.

Perhaps the first hydro-electric work in India was undertaken in 1897 near Darjeeling. The

state of Mysore constructed in 1902, the Sivasamudram hydroelectric works with an installed

capacity of 4500 kW. After independence (1947) the government of India was concerned with the

need for food for a vastly growing population and irrigation was given a much needed impetus.

Nearly 27.2% of the total outlay in the first five year plan (1951-56) was set side for irrigation and

power. In second five year plan (1956-61) , 19% of the total outlay was used for irrigation and

power. In the third five year plan (1961-66), about 22% of the total outlay was spent on irrigation

and power development.

Types Of Irrigation :

Irrigation may broadly be classified into

1. Surface irrigation

2. Sub-surface irrigation

1. Surface Irrigation :

It can be classified into:

(a) Flow Irrigation

(b) Lift Irrigation

3

When the water is available at a higher level, and it is supplied to lower level, by the more

action of gravity, then it is called Flow Irrigation. But if the water is lifted up by some

mechanical or manual means, such as pumps, etc. and then supplied for irrigation , then it is

called Lift irrigation.

Flow irrigation can be further sub divided into:

(i) Perennial irrigation

(ii) Flood irrigation

Perennial Irrigation : In perennial system of irrigation, constant and continuous water

supply is assured to the crops in accordance with the requirements of the crops, throughout

the crop period. In this system of irrigation, water is supplied through storage canal head

works and canal distribution system.

When the water is directed into the canal by constructing a weir or a barrage across the river,

it is called Direct Irrigation. Ganga canal system is an example of this type of irrigation. But

if a dam is constructed across a river to store water during monsoons, so as to supply water in

the off-taking channels during periods of low flow, then it is termed as storage irrigation.

Flood Irrigation : This kind of irrigation , is sometimes called as inundation irrigation. In

this method of irrigation, soil is kept submerged and thoroughly flooded with water, so as to

cause thorough saturation of the land. The moisture soaked by the soil, when occasionally

supplemented by natural rainfall or minor watering, brings the crop to maturity.

(2) Sub-Surface Irrigation – It is termed as sub-surface irrigation, because in this type of

irrigation , water does not wet the soil surface. The underground water nourishes the plant

roots by capillarity. It may be divided into the following two types.

(a) Natural sub irrigation and

(b) Artificial sub-irrigation.

(a) Natural sub-irrigation – Leakage water from channels, etc goes underground, and

during passage through the sub soil, it may irrigate crops, sown on lower land , by capillarity.

Sometimes , leakage causes the water table to rise up, which helps in irrigation of crops by

capillarity. When underground irrigation is achieved, simply by natural processes, without

any additional extra efforts, it is called natural sub-irrigation.

(b) Artificial sub-irrigation – When a system of open jointed drains is artificially laid

below the soil, so as to supply water to the crops by capillarity, then it is known as artificial

sub-irrigation. It is a very costly process and hence adopted in India on a very small scale.

Sometimes irrigation water may be intentionally collected in some ditches near the fields, the

percolation water may then come up to the roots through capillarity.

4

Sources Of Irrigation Water :

There are various ways in which the irrigation water can be applied to the fields. Their main

classification is as follows :

(1) Free flooding

(2) Border flooding

(3) Check flooding

(4) Basin flooding

(5) Furrow irrigation method

(6) Sprinkler irrigation method

(7) Drip irrigation method

(1) Free flooding or Ordinary Flooding – In this method, ditches are excavated in the

field, and they may be either on the contour or up and down the slope. Water from

these ditches, flows across the field. After water leaves the ditches , no attempt is

made to control the flow by means of leaves. Etc. Since the movement of water is not

restricted, it is sometimes called wild flooding. Although the initial cost of land

preparation is low, labour requirements are usually high and water application

efficiency is also low. Wild flooding, is most suitable for close growing crops,

pastures, etc. particularly where the land is steep. Contour ditches called lateral or

subsidiary ditches. Are generally spaced at about 20 to 50 metres apart, depending

upon the slope, texture of soil, crops to be grown, etc. This method may be used on

rolling land where borders , checks, basins and furrows are not feasible.

(2) Border flooding – In this method, the land is devided into a number of strips,

separated by low leaves called borders. The land areas confined in each strip is of the

order of 10 to 20 metres in width and 100 to 400metres in length. To prevent water

from concentrating on either side of the border , the land should be levelled

perpendicular to the flow. Water is made to flow from the supply ditch into each strip.

The water flows slowly towards the lower end, and infiltrates into the soil as it

advances. When the advancing water reaches the lower end of the strip, the supply of

water to the strip is turned off. The supply ditch, also called irrigation stream, may

either be in the form of an earthen channel or a lined channel or an underground

concrete pipe having risers at intervals.

(3) Check Flooding – Check flooding is similar to ordinary flooding except that the water

is controlled by surrounding the check area with low and flat levees. Levees are

5

generally constructed along the contours, having vertical interval of about 5 to 10 cm.

These levees are connected with cross – levees at convenient places. The confined

plot area varies from 0.2 to 0.8 hectare. In check flooding, the check is filled with

water at a fairly high rate and allowed to stand until the water infiltrates. This method

is suitable for more permeable soils as well as for less permeable soils, thus reducing

the percolation losses. The water can also be held on the surface for a longer time in

case of less permeable soils, for assuring adequate penetration.

(4) Basin Flooding – This method is a special type of check flooding and is adopted

specially for orchard tress. One or more trees are generally placed in the basin and the

surface is flooded as in check method by ditch water.

(5) Furrow irrigation method – In flooding methods, described above, water covers the

entire surface while in furrow irrigation method only one-fifth to one-half of the land

surface is wetted by water. It therefore results in less evaporation, less pudding of soil

and permits cultivation sooner after irrigation. Furrows are narrow field ditches,

excavated between rows of plants and carry irrigation water through them. Spacing of

furrows is determined by the proper spacing of the plants. Furrows vary from 8 to 30

cm deep, and may be as much as 400 metres long. Excessive long furrows may result

in too much percolation near the upper end. And too little water near the down slope

and. Deep furrows are widely used for row crops. Small shallow furrows called

corrugations are particularly suitable for relatively irregular topography and close

growing crops such as meadows and small grains.

(6) Sprinkler irrigation method – In this farm water application method, water is applied

to the soil in the form of a spray through a network of pipes and pumps. It is a costly

process and widely used in U.S.A. It can be used for all types of soils and for widely

different topographic and slopes. It can be used for many crops, because it fulfils the

normal requirements of uniform distribution of water. This method possesses great

potentialities for irrigation areas. This method not only costly but requires a lot of

technicalities. Special steps have to be taken for preventing entry of silt and debris,

which are very harmful for the sprinkler equipments.

(7) Drip irrigation method – Drip irrigation also called trickle irrigation is the latest field

irrigation technique and is meant for adoption at places where there exists acute

scarcity of irrigation water and other salt problems. In this methods, water is slowly

and directly applied to the root zone of the plants, thereby minimising the losses by

evaporation and percolation. This system involves laying of a system of head, mains,

6

sub-mains, laterals and drop nozzles. Water oozes out of these small drip nozzles

uniformly and at a berry small rate, directly into the plant roots areas. The head

consists of a pump to lift water, so as to produce the desired pressure of about 2.5

atmosphere, for ensuring proper flow of water through the system. The lifted

irrigation water is passed through a fertiliser tank, so as to remove the suspended

particles from the water to avoid clogging of drip nozzles. The mains and sub mains

are the specially designed small sized pipes, made of flexible material like black PVC.

These are generally buried or laid on the ground. Their sizes should be sufficient to

carry the design discharge of the system.

7

CHAPTER -2

HYDROLOGY

Hydrological Cycle:-

The water of the universe always changes from one state to other under the effect of

the sun. The water from the surface source like lakes, rivers, oceans, etc. converts to vapour

by evaporation due to solar heat. The vapour goes on accumulating continuously in the

atmosphere. This vapour is again condensed due to the sudden fall of temperature and

pressure. Thus clouds are formed. These clouds again cause the precipitation (i.e. rainfall).

Some of the vapour is converted to ice at the peak of mountains. The ice again melts in

summer and flows as rivers to meet the sea or ocean. These processes of evaporation,

precipitation and melting of ice go on continuously like an endless chain and thus a balance is

maintained in the atmosphere. This phenomenon is known as hydrologic cycle.

Ch-2.2 Precipitation or Rain Fall and its Measurement:-

From the principle of hydrologic cycle we have seen that water goes on evaporation

continuously from the water surface on earth (e.g. river, lake, sea, ocean, etc), by the effect of

sun. The water vapour goes on collecting in the atmosphere up to a certain limit. When this

limit exceeds and temperature and pressure fall to certain value, the water vapour will get

condensed and thereby cloud is formed. Ultimately droplets are formed and returned to earth

in the form of rain, snowfall, hail, etc. This is known as rain fall or precipitation.

Types of Precipitation or Rain Fall:-

Depending upon the various atmospheric conditions the precipitation may be of the

following types:

The hydrograph is a general representation of the discharge of river (in cumec)

against the time (in hr or days). The discharge is plotted as ordinate (y

plotted as abscissa (x-axis) (see the figure)

During the dry season, there is only base f

runoff. This may be shown by a line which is approximately straight (not shown in the figure)

In rainy season, at the beginning of the rainfall there is only base flow (shown by the

line AB). After some period, w

infiltration) are fulfilled, the surface runoff stars and hence the discharge of river goes on

increasing. Hence the limb of the curve rises which is called rising limb (shown by line BC).

This line reaches to the peak value at ‘C’. Again when the rain stops, the flow in the river

decreases and the limb of the curve declines. This limb is known as recession limb (as shown

by the line CD). This discharge at the point C indicates the maximum discharge

discharge or flood discharge). The total area under the curve ABCDE indicates the total

runoff. But this run off includes the base flow and the direct runoff. So, to get the actual

runoff the base flow is to be ducted by separating it from tota

1) Cyclonic Precipitation:

This type of precipitation is caused by the difference of pressure within the air mass

on the surface of the earth. If low pressure is generated at some place the warm moist air

from the surrounding area rushes to the zo

moist air rises up with whirling motion and gets condensed at higher altitude and ultimately

heavy rain fall occurs.

This may be two types.

a) Frontal Precipitation

b) Non Frontal Precipitation

a) Frontal Precipitation:-

When the moving warm moist air mass is obstructed by the zone of cold air mass, the

warm moist air rises up (as it is lighter than cold air mass) to higher altitude where it gets

condensed and heavy rainfall occurs. This is known as Frontal

b) Non Frontal Precipitation:-

When the warm moist air mass rushes to the zone of low pressure from the

surrounding area, a pocket is formed and the warm moist air rises up like a chimney towards

8

graph is a general representation of the discharge of river (in cumec)

against the time (in hr or days). The discharge is plotted as ordinate (y-axis) and the time is

axis) (see the figure)

During the dry season, there is only base flow (i.e. ground water flow) but no surface



line AB). After some period, when the initial losses (like interception, evaporation and



e reaches to the peak value at ‘C’. Again when the rain stops, the flow in the river


by the line CD). This discharge at the point C indicates the maximum discharge



runoff the base flow is to be ducted by separating it from total area.



from the surrounding area rushes to the zone of low pressure with violent force. The warm


Frontal Precipitation

Non Frontal Precipitation



condensed and heavy rainfall occurs. This is known as Frontal Precipitation.



graph is a general representation of the discharge of river (in cumec)

axis) and the time is

low (i.e. ground water flow) but no surface



hen the initial losses (like interception, evaporation and



e reaches to the peak value at ‘C’. Again when the rain stops, the flow in the river


by the line CD). This discharge at the point C indicates the maximum discharge (i.e. peak





ne of low pressure with violent force. The warm






higher altitude. At higher altitude this

is known as Non Frontal Precipitation.

2) Convective Precipitation:

In tropical counties when on a particular hot day the ground surface gets heated

unequally, the warm air is lifted to high altitude

velocity, thus, the warm moist air mass is condensed at the high altitude causing heavy rain

fall. This is known as convective precipitation (see from the figure).

2) Orographic Precipitation:

The moving warm moist air when obstructed by some mountain rises up to high

altitude, it then gets condensed and precipitation occurs. This is known as orographic

precipitation (Figure).

Hyetograph:

The graphical representation of rain fall and run

prepared with intensity of rainfall (in cm/hr) as ordinate and time (in hrs) as abscissa. The

infiltration capacity curve is drawn on this graph to show the amount of infiltration loss

(shown by dotted portion). The upper portion indicat

hatched line).

The centroid of the effective rain fall is ascertained on the graph for determination of total

run-off at any specified period.

9

higher altitude. At higher altitude this air mass gets condensed and heavy rainfall occurs. This

is known as Non Frontal Precipitation.


unequally, the warm air is lifted to high altitude and the cooler air takes its place with high


fall. This is known as convective precipitation (see from the figure).

moist air when obstructed by some mountain rises up to high


The graphical representation of rain fall and run-off is known as hyetograph. The graph is



(shown by dotted portion). The upper portion indicates the effective rainfall (shown by


air mass gets condensed and heavy rainfall occurs. This


and the cooler air takes its place with high


moist air when obstructed by some mountain rises up to high


raph. The graph is



es the effective rainfall (shown by


2.3 Measurement of Rain Fall or Precipitation:

� The instrument which is us

Raingauge.

� The principle of raingauge is that the amount of rainfall in a small area will

represent the amount of rainfall in a large area provided the metrological

characteristics of both small and large ar

Types of Rainguese :-

1) Non-Recoding Type Raingauge (Non

2) Recording Type Raingauge (Automatic)

(i) Weighing Bucket Raingauge

(ii) Tipping Bucket Raingauge

(iii) Float Type Raingauge

1) Non-Recoding Type Raingauge:

Simon’s raingauge is a non

It consists of metal casing of diameter 127mm which is set on concrete foundation A glass

bottle of capacity about 100 mm of rain fall is placed within the casing. A funnel with brass

rim is placed on the top of the bottle. The arrangement is shown:

The rainfall is recorded at every 24 hours. Generally, the measurement is taken at

8.30am every day. In case of heavy rainfall the measurement should be taken 2 to 3 times

daily so that the bottle does not overflow. To measure the amount of rainfall the glass bottle

is taken off and the collected water is measured in a measuring glass, and recorded in the

raingauge record book. When the glass bottle is taken off and it is immediately replaced wi

new bottle of same capacity.

10

2.3 Measurement of Rain Fall or Precipitation:-

The instrument which is used to measure the amount of rainfall is known as

The principle of raingauge is that the amount of rainfall in a small area will


characteristics of both small and large area are similar.

-

Recoding Type Raingauge (Non-Automatic)

Recording Type Raingauge (Automatic)

(i) Weighing Bucket Raingauge

(ii) Tipping Bucket Raingauge

(iii) Float Type Raingauge

Recoding Type Raingauge:

e is a non-recording type raingauge which is most commonly used.



s placed on the top of the bottle. The arrangement is shown:-



tle does not overflow. To measure the amount of rainfall the glass bottle


raingauge record book. When the glass bottle is taken off and it is immediately replaced wi

ed to measure the amount of rainfall is known as

The principle of raingauge is that the amount of rainfall in a small area will


recording type raingauge which is most commonly used.





tle does not overflow. To measure the amount of rainfall the glass bottle


raingauge record book. When the glass bottle is taken off and it is immediately replaced with

Figure: Simon’s Rain Gauge

2) Recoding Type Raingauge:

In this type of raingauge, the amount of rainfall is automatically recorded on a graph

proper by some mechanical device (see figure). Here, no person is required for

amount of rainfall from the container in which the rain water is collected. The recording type

raingauge may be three types.

Types of Recoding Type Raingauges:

(i) Weighing Bucket Raingauge:

bucket which is placed on pan. The pan is again fitted with some weighing mechanism. A

pencil arm is pivoted with the weighing mechanism in such a way that the movement of the

bucket can be traced by a pencil on the moving recording drum. So, when the wate

collected in the bucket the increasing weight of water is transmitted through the pencil which

traces a curve on the recording drum.the rain gauge produces a grph of cumulative rain

versus time and hence it is some time called Integrating raingau

mass curve of rain fall.

11

Figure: Simon’s Rain Gauge


proper by some mechanical device (see figure). Here, no person is required for measuring the


Types of Recoding Type Raingauges:-

(i) Weighing Bucket Raingauge: - This type of raingauge consists of a receiving



bucket can be traced by a pencil on the moving recording drum. So, when the wate


traces a curve on the recording drum.the rain gauge produces a grph of cumulative rain

versus time and hence it is some time called Integrating raingauge. The graph is known as the


measuring the


This type of raingauge consists of a receiving



bucket can be traced by a pencil on the moving recording drum. So, when the water is


traces a curve on the recording drum.the rain gauge produces a grph of cumulative rain-fall

ge. The graph is known as the

Figure :Weighing Bucket Rain Gauge

(ii) Tipping Bucket Raingauge :

in which the rain water is initially collected. The rain water then passes t

fitted to the circular collector and gets collected in two compartment tipping bucket pivoted

below the funnel. (figure).

When 0.25 mm rain water is collected in one bucket then it tips and discharges the

water in a reservoir kept below the

the funnel and the rain-water goes on collecting in it. When the requisite amount of rainwater

is collected, it also tips and discharges the water in the reservoir. In this way, a circular

motion is generated by the buckets. This circular motion is transmitted to a pen or pencil

which traces a wave like curve on the sheet mounted on a revolving drum. The total rainfall

may be ascertained from the graph. There is an opening with stopcock at bottom of

reservoir for discharging the collected rainwater. Sometimes a measuring glass is provided to

verify the results shown by the graph.

12

Figure :Weighing Bucket Rain Gauge

(ii) Tipping Bucket Raingauge :-It consists of a circular collector of diameter 30 cm

in which the rain water is initially collected. The rain water then passes through a funnel



water in a reservoir kept below the buckets. At the same time the other bucket s comes below

water goes on collecting in it. When the requisite amount of rainwater


generated by the buckets. This circular motion is transmitted to a pen or pencil


may be ascertained from the graph. There is an opening with stopcock at bottom of


verify the results shown by the graph.

It consists of a circular collector of diameter 30 cm

hrough a funnel



buckets. At the same time the other bucket s comes below

water goes on collecting in it. When the requisite amount of rainwater


generated by the buckets. This circular motion is transmitted to a pen or pencil


may be ascertained from the graph. There is an opening with stopcock at bottom of the


Figure :

(ii) Float Type Raingauge :

rectangular container and rotating recording drum is drum is provided at the another end. The

rain water enters the container through the funnel. A float is provided within the container

which rises up as the rain water gets collected there. The float

contains a pen arm for recoding the amount of rainfall on the graph paper dropped on the

recording drum. It consists of a siphon which starts functioning when the float rises to some

definite height and the container goes on emptyi

Selection of Site for Raingauge Station:

while selecting a site for rain gauge station.

a) The site should be on level ground and on open space. It should never be sloping

ground.

b) The site should be such that the distance between the gauge station and the objects

(like tree, building etc) should be atleast twice the height of the objects.

c) In hilly area, where absolutely level ground is not available, the site should be so

selected that the station may

d) The site should be easily accessible to the observer.

e) The site should be well protected from cattles by wire fencing.

13

Figure :- Tipping Bucket Raingauge

(ii) Float Type Raingauge :-In this type rain gauge a funnel is provided at one en



which rises up as the rain water gets collected there. The float consists of a rod which



definite height and the container goes on emptying gradually

Selection of Site for Raingauge Station:- The following points should be considered

while selecting a site for rain gauge station.

The site should be on level ground and on open space. It should never be sloping

uch that the distance between the gauge station and the objects

(like tree, building etc) should be atleast twice the height of the objects.

In hilly area, where absolutely level ground is not available, the site should be so

selected that the station may be well shielded from high wind.

The site should be easily accessible to the observer.

The site should be well protected from cattles by wire fencing.

In this type rain gauge a funnel is provided at one end of



consists of a rod which



The following points should be considered

The site should be on level ground and on open space. It should never be sloping

uch that the distance between the gauge station and the objects

In hilly area, where absolutely level ground is not available, the site should be so

14

Ch-2.4

Run-off:-

Runoff or Surface run-off in hydrology, the quantity of water discharged in surface

streams. Runoff includes not only the waters that travel over the land surface and through

channels to reach a stream but also interflow, the water that infiltrates the soil surface and

travels by means of gravity toward a stream channel (always above the main groundwater

level) and eventually empties into the channel. Runoff also includes ground water that is

discharged into a stream; stream flow that is composed entirely of groundwater is termed

base flow, or fair-weather runoff, and it occurs where a stream channel intersects the water

table.

The total Runoff is equal to the Total precipitation less the losses caused by

evapotranspiration (loss to the atmosphere from soil surfaces and plant leaves), storage (as in

temporary ponds) and other such abstractions.

Catchment Area:-A hydrological catchment is defined as the area of land point (usually the

sea). A hydrological catchment can vary widely in size and other characteristics such as

height above sea level, slope, geology and land use, and may contain different combination of

freshwater bodies (surface water and ground water) and coastal waters.

Estimation of Flood Discharge:-

The flood discharge may be estimated by the below mentioned methods.

(a) Dicken’s Formula

Q= C X A 3/4

Where Q= Discharge in cumec

A= Catchment area in sq. km

C= a constant depending upon the factors affecting flood discharge

** An average value of C considered as 11.5

(b) Ryve’s Formula

Q= C X A 2/3

Where Q= Discharge in cumec

A= Catchment area in sq. km

C= a constant

** An average value of C considered as 6.8

Ch-2.5

Hydrograph:-

The hydrograph is a graphical representation of the discharge of river (in cumec) against the

time (in hr or days). The discharge is plotted as ordinate (y-axis) and the time is plotted as

abscissa (x-axis).

During the dry season, there is only base flow (i.e. ground flow) but no surface runoff. This

may be shown by a line which is approximately straight (not shown in the figure).

In rainy season, at the beginning of the rainfall there is only base flow (shown by the line

AB). After some period, when the initial losses (like interception, evaporation and

infiltration) are fulfilled, the surface runoff starts and hence the discharge of river goes

increasing. Hence the limb of the curve rises which i

BC). This line reaches to the peak value at ‘C’. Again when the rain stops, the flow in the

river decreases and the limb of te curve declines. This limb is known as recession limb (as

shown by the line CD). The disch

(i.epeak discharge or flood discharge). The total area under the curve ABCDE indicates the

total runoff. But this run off includes the base flow and the direct runoff. So, to get the actual

runoff the base flow is to be deducted by separating it from total area.

Unit Hydrograph:-

A unit hydrograph may be defined as a hydrograph which is obtained from one cm of

effective rainfall (i.e. run-off) for unit duration. Here, effective rainfall means the rainf

excess (i.e. run-off) which directly flows to the river or stream. The unit duration is the period

during which the effective rainfall is assumed to be uniformly distributed. The unit duration

may be considered as 1 hr, 2 hr, 3 hr, 4 hr, …. Etc. as for

prepared for as effective rainfall of one cm lasting for 2 hrs, then it is known as 2 hr. unit

hydrograph, for the duration of 3 hrs it known as 3 hr unit hydrograph )as sowon in the figure

15

increasing. Hence the limb of the curve rises which is called rising limb (shown by the line



shown by the line CD). The discharge at the point C indicates the maximum discharge



e flow is to be deducted by separating it from total area.


off) for unit duration. Here, effective rainfall means the rainf

off) which directly flows to the river or stream. The unit duration is the period


may be considered as 1 hr, 2 hr, 3 hr, 4 hr, …. Etc. as for example, if a hydrograph is



s called rising limb (shown by the line



arge at the point C indicates the maximum discharge




off) for unit duration. Here, effective rainfall means the rainfall

off) which directly flows to the river or stream. The unit duration is the period


example, if a hydrograph is



16

Concept of Unit Hydrograph: - The unit hydrograph theory is based on the conception that

if two identical storms occur on a drainage basin with identical condition, then unit

hydrograph of runoff from the two storms may be expected as same. This conception of unit

hydrograph was first given by L.K. Sherman in 1932.

CHAPTER 3

17

CHAPTER-3

WATER REQUIREMENTS OF CROPS

3.1 CROP SEASONS:-

The period during which some particular types of crops can be grown every year on the same

land is known as crop seasons. The following are the main crop seasons.

• Kharif season: - this seasons ranges from June to October. The crops are sown in the

very beginning of monsoon and harvested at the end of autumn. Ex- rice, millet, jute,

groundnut, etc.

• Rabi seasons: - this season ranges from October to March. The crops are sown in the

very beginning of winter & harvested at the end of spring. Ex- wheat, gram, mustard,

onion, etc.

3.2 DUTY:-

• The duty of water is defined as number of hectares that can be irrigated by constant

supply of water at the rate of one cumec throughout the base period.

• It is expressed in hectares/cumec.

• It is denoted by ”D”.

• The duties of some common crops are

Crop duty in hectares/cumec

Rice 900

Wheat 1800

Cotton 1400

Sugarcane 800

DELTA:-

• Each crop requires certain amount of water per hectare for its maturity. It is the total

amount of water supplied to the crop(from 1st watering to last watering) is stored on

the land without loss, then there will be a thick layer of water standing on the land.

This depth of water layer is known as delta.

• It is denoted by ∆.

• It is expressed in cm.

Kharif crop Delta in cm

18

Rice 125

Maize 45

Ground nut 30

Millet 30

Rabi crop delta in cm

Wheat 40

Mustard 45

Gram 30

Potato 75

BASE:-

• Base period is the whole period from irrigation water first watering for preparation of

the ground for planting the crop to its last watering before harvesting.

• It is denoted by “B”.

• It is expressed in days.

Crop Base in days

Rice 120

Wheat 120

Maize 100

Cotton 200

Sugarcane 320

Relation between base duty and delta:-

Let ,

D =duty of water in hectares/cumec

B =base in days,

∆ =delta in m

From definition, one cumec of water flowing continuously for “B” days gives a depth of

water ∆ over an area D hectares. That is

1 cumec for B days gives ∆ over D/B hectares

1 cumec for 1 days gives ∆ over D/B hectares

1 cumec-day =D/B*∆ hectare-meter

Again, 1 cumec-days = 1*24*60*60=86400m

Problem 1:- a channel is to be designed for irrigating 5000 hectares in kharif crop &

4000 hectares in rabi crop. The wa

cm, respectively. The kor period for kharif is 3 weeks & for rabi is 4weeks.

Determine the discharge of the channel for which it is to be designed.

Solution:-

∆=8.64B/D

Discharge for kharif crop:

∆=60cm=0.60m

B=3weeks=21days

Duty=(8.64*21)/0.60=302.4 hectares/cumec

Area to be irrigated =5000 hectares

Required discharge of channel=5000/302.4=16.53cumec

Discharge for rabi crop:-

∆=25cm=0.25m

B=4weeks=28 days




19

days = 1*24*60*60=86400m3

a channel is to be designed for irrigating 5000 hectares in kharif crop &

4000 hectares in rabi crop. The water requirement for kharif & rabi are 60 cm & 25


Determine the discharge of the channel for which it is to be designed.

Discharge for kharif crop:-





be irrigated =4000 hectares


a channel is to be designed for irrigating 5000 hectares in kharif crop &

ter requirement for kharif & rabi are 60 cm & 25


20

Problem 2:- the command area of a channel 4000 hectares. The intensity of irrigation

of a crop is 70%. The crop requires 60 cm of water in 15 days, when the effective

rainfall is recorded as a 15cm during that period. Find,

a) the duty at the head of field.

b) the duty at the head of field.

c) The head discharge at the head of channel.

Assume total losses as 15%.

Solution:-

Depth of water required =60 cm

Effective rain fall =15cm

Depth of irrigation water = 60-15=45cm

Delta =45cm=0.45m, B = 15days

From relation, ∆ =(8.64*B)/D

Duty D = (8.64*15)/0.45 =288 hectares/cumec

a) So, duty at the head of field =288 ha/cumec. Due to the losses of water the

duty at the head of the channel will be reduced. here losses are 15%.

b) So, the duty at the head of channel = 288*(85/100) =244.80 hect/cumec.

c) Total area under crop =4000 * (70/100) =2800 hect

The discharge at the head of channel = 2800/244.8=11.438 cumec.

3.3 GROSS COMMAND AREA:-

The whole area enclosed between an imaginary boundary line which can be included

in an irrigation project for supplying water to agricultural land by the networks of

canal is known as gross command area. It includes both the culturable & unculturable

area.

unculturable area:-

the area where the agriculture cannot be done & crop cannot be grown is known as

unculturable area.

culturable area:-

the area where the agriculture can be done satisfactory is known as culturable area

CULTURABLE COMMAND AREA:-

21

The total area within an irrigation project where the cultivation can be done & crops

can be grown is known as culturable command area. again c.c.a may be of two

categories.

a) Culturable cultivated area:- it is the area within c.c.a where the cultivation

has been actually done at present.

b) Culturable uncultivated area:- it is the area within c.c.a where the

cultivation is possible but is not being cultivated at present due to some

reasons.

INTENSITY OF IRRIGATION:-

• The total culturable command area may not be cultivated at the same time in a

year due to various reasons. Some area may remains vacant every year. Again

various crops may be cultivated in the culuturable command area. So, The

intensity of irrigation may be defined as a ratio of cultivated land for a

particular crop to the total culturable command area.

• It is expressed as a percentage of c.c.a.

FIELD CAPACITY:-

The field capacity is defined as the amount of maximum moisture that can be held by

the soil against gravity.

PERMANENT WILTING POINT:-

It is defined as the amount of moisture held by soil which cannot be extracted by the

roots for transpiration. At this point the wilting of the plant occurs. It is also expressed

in percentage.

FREQUENCY OF IRRIGATION

The irrigation water is applied to the field to raise the moisture content of the soil up

to its field capacity. The application of water is then stopped. The water content also

reduces gradually due to transpiration and evaporation. If the moisture content is

dropped below the requisite amount, the growth of the plants gets disturbed. So the

moisture content requires to the immediately replenished by irrigation and it should

22

be raised to the field capacity. The frequency of irrigation should be worked out in

advance so that it can be applied in proper intervals.

a. The frequency of irrigation may be ascertained by the following expressions,

Dw=�� × �

�� × �F − M�

where, Dw = Depth of water to be applied in each watering;

d = Depth of root zone

Ws= Unit wt. of soil;

Ww = Unit wt. of water;

Fc = Field capacity;

M0 = Optimum moisture content.

b. fw = ��

��

Where. fw = Frequency of watering;

Dw = Depth of water to be applied in each watering;

Cu = Daily consumptive use of water.

23

CHAPTER 4

FLOW IRRIGATION

DEFINATION:-

The irrigation system in which the water flows under gravity from the source to

agricultural land is known as flow irrigation

PERENNIAL IRRIGATION:-

• In this irrigation water is available throught the year. Hydraulic structures are

necessary across the river for raising the water level.

• Large area can be included under this system

• Negligible silting takes place in the canal bed

TYPES OF CANAL:-

1. BASED ON THE PURPOSE:-

Based on the purpose of service, the canals are 4 types

a) Irrigation canal:-the canal which is constructed to carry water from the source to the

agricultural land for the purpose of irrigation is known as irrigation canal.

b) Navigation canal:-the canal which is constructed for the purpose of inland navigation

is known as navigation canal.

c) Power canal:-the canal which is constructed to supply water with very high force to

the hydroelectric power station for the purpose of moving turbine to generate electric

power is known as power canal.

d) Feeder canal:- the canal which is constructed to feed another canal or river for the

purpose of irrigation or navigation is known as feeder canal

2. BASED ON THE NATURE OF SUPPLY:-

Based on the nature of supply the canal are 2 types

a) Inundation canal:- the canal which is excavated from the banks of the inundation

river to carry the water to agricultural land in rainy season only is known as

inundation canal.

b) Perennial canal:-the canal which can supply water to the agricultural land

throughout the year is known as perennial canal.

3. BASED ON DISCHARGE:-

According to discharge capacity the canals are

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a) Main canal:-the large canal which is taken directly from the diversion head work or

from the storage to supply water to the network of the small canal is known as main

canal.

b) Branch canal:-the branch canals are taken from either side of the main canal at

suitable points so that the whole command area can be covered by the network

c) Distributory channel:- these channels are taken from the branch canals to supply

water to different sectors.

d) Field channel:- these channels are taken from the outlets of the distributory channel

by the cultivators to supply water to their own lands.

4. BASED ON ALLIGNMENT:-

Depending upon the alignment the canal are following types

a) Ridge or water shed canal:- the canal which is aligned along the ridge line is known

as ridge canal.

b) Contour canal:- the canal which is aligned approximately parallel to the contour

lines is known as contour canal.

c) Side slope canal:-the canal which is aligned approximately at right angle to the

contour lines is known as side slope canal.

CANAL SECTION

TERMS RELATED TO CANAL SECTION:

1. Canal bank

2. Berm

3. Hydraulic gradient

4. Counter berm

5. Free board

6. Side slope

7. Service road or inspection road

8. Dowel or Dowla

9. Borrow pit

10. Spoil bank

11. Land width

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canal section

CANAL BANK:

The canal bank is necessary to retain water in the canal to the full supply

level. According to different site conditions the bank of the canals are two types..

(a) Canal bank in cutting :

The banks are constructed on both side of the canal to provide only a

inspection load. The side slope will be 1.5:1 or 2:1 according to the nature of soil.

(b) Canal bank in full banking:

Both canal banks are constructed above the ground level. The height of

the bank will be high and the section will be large due to hydraulic gradient.

BERM:

The distance between toe of the bank and the top edge of the cutting is called

berm.

The berm is provided for following reasons:

(a) To protect the bank from erosion.

(b) To provide a space for widening the canal section in future if necessary.

(c) To protect the bank from sliding down towards the canal section.

(d) The silt deposition on the berm makes an impervious lining.

(e) If necessary borrow pit can be excavated on the berm.

The width of the berm varies from D to 2D.where D is the full supply level

HYDRAULIC GRADIENT:

When water is retained by the canal bank, the seepage occurs through the body of the

bank. Due to the resistance of soil, the saturation line forms a sloping line which may pass

through countryside of the bank. The sloping line is known as hydraulic gradient.

26

SOIL H.G Clayey soil 1:4

Sandy soil 1:6

Alluvial soil 1:5

COUNTER BERM:

When the water is retain by a canal bank the hydraulic gradient line passes through the

body of the bank. The gradient should not intersect the outer side of the bank. It should pass

through the base and a minimum cover of 0.5m should always be maintained. It may occur

that the hydraulic gradient line intersect the outer side of the bank in that case a projection is

provided on the bank to obtain minimum cover. This projection is known as counter berm.

FREE BOARD:

It is the distance between the full supply level and top of the bank. The amount of free

board varies from 0.6 m to 0.75 m.

It is provided for the following reasons

(a) To keep a sufficient margin so that the canal water does not overtop the bank.

(b) To keep the saturation gradient much below the top of the bank

SIDE SLOPE:

The side slope of the canal bank and canal section depends upon the angle of repose

of the soil existing on side. So to determine the side slope of different sections the soil

sample should be collected from the site and should be tested in the soil testing laboratory.

Permissible side slope for some soil

Types of soil Side slope in cutting Side slope in banking

Clayey soil 1:1 1 ½:1

Alluvial soil 1:1 2:1

Sandy loam 1 ½:1 2:1

Sandy soil 2:1 3:1

SERVICE ROAD:

The road is provided on the top of the canal bank for inspection and maintenance

work is known as service road or inspection road. For main canal the service road are

provided on both side of the bank but for branch canal the road is provided on the bank only.

The width of the service road for main canal varies from 3-4 m. But finally these roads serve

the purpose of communication between different villages.

DOWEL:

27

The protective small embankment which is provided on the canal side of the service

road for safety of the vehicles playing on it is known as dowel or dowla. The top width is

generally 0.5m and the height above the road level is about 0.5m.

SPOIL BANK:

When the canal is constructed in pool cutting the excavated earth may not be sufficient

for forming the bank. In such case the extra earth is deposited in the form of small bank

which is known as spoil bank. The spoil banks are provided on one side or both side of the

canal bank depending upon the quantity of extra earth and available space. The spoil bank

are not continuous sufficient space are left between the adjacent spoil banks for proper

drainage.

BORROWPIT:

When the canal is constructed in practically cutting and partial banking, the

excavated earth may not be sufficient for forming the required bank. In such case, the extra

earth required for the construction of banks is taken from some pits which are known as

borrow pits. The borrow pit may be inside or outside of the canal. The maximum depth

should be 1m. The excavation is done in a no of borrow pit living a gap between them. The

gap is generally half of the length of each borrow pit.

LAND WIDTH:

The total land width required for construction of canal depends upon the nature of site

condition. Such as fully in cutting of fully in banking or partially in cutting and partially in

banking. To determine the total width the following dimension should be added.

(a) Top width of the canal.

(b) Twice the berm width.

(c) Twice the bottom width of banks.

(d) A margin of one meter from the heel of the bank on both sides.

(e) Width of the external borrow pit if any

(f) A margin of 0.5m from the outer edge of borrow pit on both sides, if external

borrow pit becomes necessary.

BALANCING DEPTH:

If the quantity of excavated earth can be fully utilized when making the bank on both

side then that canal section is known as economical section. The depth of cutting for the idle

condition is known as balancing depth.

SKETCHES OF DIFFERENT CANAL CROSS-SECTION:-

Canal in full cutting:-

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canal in partially cutting & partially banking:-

canal in fully bankin:-

CANAL LINING

OBJECTS OF CANAL LINING:

(a) To control seepage.

(b) To prevent water logging.

(c) To increase the capacity of canal.

(d) To increase the command area.

(e) To protect the canal from damage by flood.

(f) To control the growth of weeds.

ADVANTAGES OF CANAL LINING:

(a) It reduces the loss of water due to seepage and hence the duty is enhanced.

(b) It controls the water logging and hence the bad effects of water logging are eliminated.

(c) It provides smooth surface and hence the velocity of flow can be increased.

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(d) Due to increased velocity the discharge capacity of a canal is also increased.

(e) Due to increased velocity, the evaporation loss also be reduced.

(f) It eliminates the effect of scouring in the canal bed.

(g) The increased velocity eliminates the possibility of silting in the canal bed.

(h) It controls the growth of weeds along the canal sides and bed.

(i) It provides the stable section of the canal.

(j) It reduces the requirement of land width for the canal, because smaller section of the

canal can produce greater discharge.

(k) It prevents the sub soil salt to come in contact with the canal water.

(l) It reduces the maintenance cost of canals.

DISADVANTAGES:

(a) The initial cost of canal lining is very high

(b) It take too much time to complete the project work

(c) It involves much difficulties for repairing of damaged section of line

(d) It becomes difficult if the outlet are required to be shifted or new outlet are requred to

be provided

TYPES OF LINING:

The following are the types of lining according to their site condition

(1) Cement concrete lining

(2) Pre-cast concrete lining

(3) Cement mortar lining

(4) Lime concrete lining

(5) Brick lining

(6) Boulder lining

(7) Shot crete lining

(8) Asphalt lining

(9) Bentonite and clay lining

(10) Soil-cement lining

1. CEMENT CONCRETE LINING :

30

This type of lining is recommended for canal in full banking. It is widely

accepted as best impervious lining. The velocity of flow may be kept above 2.3 m/sec. It can

eliminate completely growth of weeds.

Following are the steps for cement concrete lining…..

(A) Preparation of sub-grade :

The subgrade is prepared by ramming the surface properly with a layer of

sand(about 15cm) . then a slurry of cement and sand (1:3) is spread uniformly over

the prepared bed.

(B) Laying of concrete :

The cement concrete of grade M15 is spread uniformly according to desire

thickness (100-150mm). after laying the concrete is tapped until the slurry comes on

the top . then the curing is done for two weeks..

2. PRE-CAST CONCRETE LINING :

The lining is recommended for the canal in full banking. It consist of pre

cast concrete slabs of size (60cm*60cm*5cm) which are set along the canal bank and

bed with cement mortar (1:6). A network of 6mm dia. rod is provided in the slab with

spacing 10cm centre of centre. Expansion joints are also provided. The slabs are set in

the following sequence,

(a) The sub grade is prepared by properly ramming the soil with a layer of sand.

(b) The slabs are stacked as per estimate along the course of the canal.

(c) The curing is done for a week.

3. CEMENT MORTAR LINING

This type of lining is recommended for the canal fully in cutting where

hard soil or clayey soil is available. The thickness of cement mortar(1:4) is generally

2.5cm. This lining is impervious, but is not durable. The curing should be done

properly.

4. LIME CONCRETE LINING

When hydraulic lime, surkhi and brick ballast are available in plenty along the

course of the canal or in the vicinity of the irrigation project, then the lining of the

canal may be made by the lime concrete of proportion 1:1:6. The thickness of

concrete varies from 150mm to 225mm and the curing should be done for longer

period. This lining is less durable then the cement concrete lining.

31

5. BRICK LINING

This lining is prepared by double layer brick flat soling laid with cement

mortar (1:6) over the compacted sub grade. The first class bricks should be

recommended for the work. The curing should be done properly. The lining is

preferred for following reasons

(a) The lining is economical

(b) Work can be done very quickly

(c) Repair work can be done easily

(d) Brick can be manufactured from the excavated earth near the site

DISADVANTAGES

(a) It is completely impervious

(b) It has low resistance against erosion

(c) It is not so much durable

6. BOULDER LINING

In hilly areas where the boulders are available in plenty, this type of

lining is generally recommended. The boulders are laid in single or double layer

maintaining the slope of the banks and the level of the canal. The lining is very

durable and impervious. But the transporting cost of material is very high. So ,it

cannot be recommended for all cases.

7. SHOT CRETE LINING

In this system, the cement mortar is directly applied on the sub grade

by equipment known as cement gun. The mortar is termed as shot crete and the lining

is known as shot crete lining. The process is also known as guniting, as a gun is used

for laying the mortar. The line is done in two ways..

(A) By dry mix :

A mixture of cement and moist sand is prepared and loaded in the

cement gun. Then it is forced through the nozzle of the gun with the help of

compressed air. The mortar spreads over the sub grade to a thickness which

varies from 2.5 cm to 5 cm.

(B) By wet mix :

32

The mixture of cement ,sand and water is prepared according to the

approved consistency. The mixture is loaded in the gun and forced on the

sub-grade… This type of lining is very costly and is not durable.

8. ASPHALT LINING

This lining is prepared by spraying asphalt at a very high

temperature (about150’) on the subgrade to a thick varies from 3mm to 6mm. the hot

asphalt when becomes cold forms a water proof membrane over the sub grade. This

membrane is covered with a layer of earth and gravel. The lining is very cheap

9. BENTONITE AND CLAY LINING

A mixture of benotite and clay are mixed to gather to form a sticky

mass. The mass is spread over the sub-grade to form an impervious membrane which

is effective in controlling the seepage of water, but it cannot control the growth of

weeds. This lining is recommended for small channels.

10. SOIL-CEMENT LINING

This lining is prepared with a mixture of soil and cement. The usual

quantity of cement is10 percent of the weight of dry soil. The soil and cement are

thoroughly mixed to get an uniform texture. The mixture is laid on the surface of the

sub-grade and it is made thoroughly compact. The lining is efficient to control the

seepage of water, but it cannot control the growth of weeds. So this is recommended

for small channels only.

SELECTION OF TYPES OF LINING :

(A) Imperviousness

(B) Smoothness

(C) Durability

(D) Economy

(E) Sitecondition

(F) Life of project

33

CHAPTER-5

WATER LOGGING

Definition:-

In the agricultural land, when the soil pores within the root zone of the crops

get saturated with the sub soil water , the air circulation inside the soil pores gets totally

stopped . This phenomenon is called as water logging.

The water logging makes the soil alkaline in character and the fertility of the

land is totally destroyed and the yield crops gets reduced.

Due to heavy rain fall for a longer period or due to continuous percolation of

the water from the canals, the water table gets raised near the surface of the soil. Then by

capillary action then the water rises to the root zone of the crops and goes on saturating

soil.

Causes of the Water Logging:-

The Following are the main causes of the water Logging.:-

� Over Irrigation:-In inundation irrigation since there is no controlling system of water

supply it may cause over irrigation. The excess water percolates and remains stored

within the root zone of the crops. Again in perennial irrigation system if water is

supplied more than its required. This excess water is responsible for water logging.

� Seepage from Canals:-In unlined canal system ,the water percolates through the

bank of the canals and get collected in low lying area along course of the canal and

thus water table gets raised. This seepage more in case of canal in banking.

� Inadequate Surface Drainage:- When the rainfall is heavy and there is no proper

provision of surface drainage then the water gets collected and submerges in the

vast area. When this condition continues for a longer period the water table is

raised.

� Obstruction in natural water courses:-If the bridges and the culverts are constructed

across a water courses with the opening with insufficient discharge capacity the

upstream area gets flooded and this causes water logging.

34

� Obstruction in sub soil drainage:- If some impermeable stratum exists in a lower

depth below the ground surface then the movement of the subsoil water gets

obstructed and causes the water logging in the area.

� Nature of the Soil:- The soil of low permeability like Black cotton soil does not allow

the water to percolate through it So, in case of over irrigation or flood the water

retains in this type of land and causes water logging.

� Seepage from reservoir:- If the reservoir basin consists of permeable zones cracks

and fissures which are not detected during the construction of dam, these may

cause seepage of the water. This subsoil water will move towards the low lying areas

causes the water logging.

� Incorrect method of cultivation:- if the agricultural land is not well leveled and there

is no arrangement of surplus for the water to flow out then it will create the pools of

the stagnant water leading to water logging.

� Poor irrigation Management:- If the main canal is kept or long period unnecessarily

without computing the total water requirement of the crops then this leads to the

over irrigation which may causes water logging.

� Excessive rainfall :- If the rainfall is excessive and water gets no time to get drained

off completely then a pool of stagnant water leading to water logging.

� Topography of the land:- If the agricultural land is flat i.e with no country slope and

consists of depression or undulation then this leads to water logging.

� Occasional Flood:- If an area gets affected by flood every year and there is no

proper drainage system the water table gets raised and this causes water logging.

Effects of Water logging:-

The following effects of the water logging.

� Stalinization of the Soil:- Due to the water logging the dissolved salts like

sodium carbonate, sodium chloride and sodium sulphate come to the surface of the

soil. When the water evaporates from the surface,the salts are deposited there. This

process is known as Stalinization of the soil. Excessive concentration of the salt

makes the land alkaline, it does not allow the plant to strive and thus the yield of the

crop is reduced.

� Lack of Aeration:- The crops required some nutrients for the growth which are

supplied some bacteria and some micro organism by breaking the complex

nitrogenous compound into simple compounds which are consumed by the plants

for the growths. But the bacteria required the oxygen for their life and activity.

When the aeration of the soil is stopped by the water logging these bacteria cannot

35

survive without oxygen and the fertility of the land is lost which results in reduction

of yield.

� Fall of Soil Temperature:-Due to the water logging the soil temperature is

lowered. At low temperature of the soil the activity of the bacteria becomes very

slow and consequently the plant do not get requisite amount of food in time. Thus

the growth of the plant is hampered and the yield is reduced.

� Growth of weeds and aquatic plants:-Due to the water logging the

agricultural land is converted to marshy land and the weeds and the aquatic plants

are grown in plenty. This plants consume the soil food in advance and thus the crops

gets destroyed.

� Disease of the crops:-Due to the low temperature and poor aeration the crops

gets some disease which may destroy the crops or reduce the yield.

� Difficulty in cultivation:-In water logged area it is very difficult to carry out the

operation of cultivation such as tilling, ploughing etc.

� Restriction of the root Growth:-When the water table rises near to root zone

the soil gets saturated .The growth of the root is confirmed only to the top layer of

the soil. So, the crops cannot be matured properly and the yield is reduced.

Control of Water Logging:-

The following measures may be taken to control the water logging.

Prevention of Percolation from Canals:- The irrigation canals should be lined

with impervious lining to prevent the percolation through the bed and banks of the

canals. Thus the water logging may be controlled. Intercepting the drains may be

provided along the course of the irrigation canals in place where percolation of

water is detected.

Prevention of Percolation from Reservoirs:-During the construction of dam

the geological survey should be conducted on the reservoir basin to detect the zone

permeable formation through which may percolate. These zones should be treated

properly to prevent the seepage .If afterwards it is found that there is still leakage of

water through some zone then sheet piling should be done to prevent the leakage.

Economical use of water:- If water is used economically then it may control the

water logging and the yields crops may be high. So, the special training should be

given to the cultivators to release the benefits of economical use of water.

Control of Intensity of Irrigation:- The intensity of irrigation may cause the

water logging so it may be controlled in a planned way so that there is no possibility

of water logging in a particular area.

36

Fixing of Crop pattern:- Soil survey should be conducted to fix the crop pattern.

The crops having high rate of evapotranspiration should be recommended for the

area susceptible to water logging.

Providing Drainage System:- Suitable drainage system should be provided in

the low lying area so that the rain water does not stand for long period

Improvement of natural Drainage:- Sometimes the natural drainage may be

completely silted up or obstructed by weeds aquatic plants etc. The effected section

of the drainage should be improved by excavating and clearing the obstruction.

Pumping of Ground Water:- A no. of open wells or tube wells are constructed

in water logged area and the ground water is pumped out until the water table goes

down to a safe level.

Construction of Sump Wells:- Sump wells may be constructed with in the water

logged area and they help to collect the surface water. The water from the slump

wells may be pumped to the irrigable lands or may be discharged to any river.

DIVERSION HEAD WORKS AND REGULATORY STRUCTURES

Introduction

Any hydraulic structure which supplies water to the off

headwork. Head work may be divided into two classes such as:

(a) Diversion Head Work and (b) Storage Head Work

(a) Diversion Head

required supply into the canal from the river.

(b) Storage Head Work :

the river. It stores water during the period of excess supplies in the river &

releases it when demand overtakes available supplies.

Necessity of Diversion Head Work :

(1) The necessity of diversion head works in the irrigation projects is to divert the river

water into the canal and a constant and continuous water supply is ensured into

canal even during the periods of low flow.

(2) It controls the silt entry into the canal.

(3) It raises the water level in the river so that the commanded area can be increased.

(4) It reduces fluctuations in the level of supply in the river.

(5) It regulates the intake of water into the canal.

(6) It stores water for tiding over small periods of short supplies.

General layout and different part of a Diversion Head Work

37

CHAPTER- 6

N HEAD WORKS AND REGULATORY STRUCTURES

Any hydraulic structure which supplies water to the off-taking canal is called a

headwork. Head work may be divided into two classes such as:

Diversion Head Work and (b) Storage Head Work

Diversion Head Work : A diversion head work is that which divert the

required supply into the canal from the river.

Storage Head Work :A storage head work is the construction of a dam across


eleases it when demand overtakes available supplies.

Necessity of Diversion Head Work :

The necessity of diversion head works in the irrigation projects is to divert the river

water into the canal and a constant and continuous water supply is ensured into

canal even during the periods of low flow.

It controls the silt entry into the canal.

It raises the water level in the river so that the commanded area can be increased.

It reduces fluctuations in the level of supply in the river.

ake of water into the canal.

It stores water for tiding over small periods of short supplies.

General layout and different part of a Diversion Head Work

N HEAD WORKS AND REGULATORY STRUCTURES

taking canal is called a

A diversion head work is that which divert the

A storage head work is the construction of a dam across


The necessity of diversion head works in the irrigation projects is to divert the river

water into the canal and a constant and continuous water supply is ensured into the

It raises the water level in the river so that the commanded area can be increased.

38

( Fig.1Layout of a diversion head work)

Divide Wall :A divide wall is constructed parallel to the direction of flow of river to separate

the weir section and the under sluices section to avoid across flows. If there are under sluices

at both the sided, there are 2 divide walls.

Scouring sluices : Provide adjacent to the canal head regulator should be able to pass fair

weather flow for which the crest shutters on the weir proper need not be dropped.

Fish Ladder : A passage provided adjacent to the divide wall on the weir side for the fish to

travel from up stream to down stream and vice versa. Fish migrate upstream or down stream

in search of food or to rich their spreading places.

Guide Banks : Guide Banks are provided on either side of the diversion head work for a

smooth approach and to prevent the river from outflanking.

Marginal bunds : Marginal bunds are provided on either side of the river up stream of

diversion head works to protect the land and property which is likely to be submerged during

ponding of water in floods.

Head regulators : A canal head regulator is provided at the head of the canal off taking from

the diversion headwork. It regulates the supply of water into the canal, controls the entry silt

into the canal and prevents the entry of river flood into canal.

A diversion head work is further divided in to two parts:

(a) Weir :

� The weir is a solid obstruction put across the river to raise its water level and

divert the water in to the canal.

� Here the water level is raised up to the required height and the surplus water is

allowed to flow over the weir.

� Generally it is constructed across an inundation river. Weirs are commonly used

to alter the flow of rivers to prevent flooding, measure discharge and help render

rivers navigable.

� If a weir also stores water for tiding over small periods of short supplies, it is

called a storage weir.

� The main difference between a storage weir and a dam is only in height and the

duration for which the storage is stored. A dam stores the supply for a

comparatively longer duration.

(b)Barrage :

� The function of barrage is s

effected by the gates alone.

� It consists of a number of large gates that can be opened or closed to control the

amount of water passing through the structure and thus regulate and stabilise river

water.

� No solid obstruction is put across the river. The crest level in the barrage is kept at a

low level. During the floods the gates are raised to clear off the high flood level,

enabling the high flood to pass downstream with minimum afflux. When the flood

recedes, the gates are lowered and the flow is obstructed, thus raising the water level

to the upstream of the barrage.

� Due to this, there is less silting and better control over the levels.

39

main difference between a storage weir and a dam is only in height and the


comparatively longer duration.

(fig.2 Vertical drop wier)

The function of barrage is similar to that of a weir but the heading up of water is

effected by the gates alone.

It consists of a number of large gates that can be opened or closed to control the


No solid obstruction is put across the river. The crest level in the barrage is kept at a




to the upstream of the barrage.

Due to this, there is less silting and better control over the levels.

main difference between a storage weir and a dam is only in height and the


imilar to that of a weir but the heading up of water is

It consists of a number of large gates that can be opened or closed to control the


No solid obstruction is put across the river. The crest level in the barrage is kept at a




40

(fig.3 barrage)

Differences between Weir and Barrage :

Barrage Weir

� Low set crest

� Gated over entire length

� Gates are of greater height

� Gates are raised clear off the high

floods

� Perfect control on river flow

� Longer construction period

� Costly structure

� Silt removal is done through

under sluices

� High set crest

� Shutters in part length

� Shutters are of smaller height

� Shutters are dropped to pass

floods

� No control of river in low floods

� Shorter construction period

� Relatively cheaper structure

� No means for silt disposal

Functions of Regulatory structures :

A regulatory structure is provided at the head of the off- taking canal and serves the

following functions.

(1) It regulates the supply of water entering the canal.

(2) It controls the entry of silt in the canal.

(3) It prevents the river floods from entering the canal.

Head Regulators and Cross regulators :

Head regulators and cross regulators regulate the supplies of the off-taking channel

and parent channel respectively. The distributary head regulator is provided at the head of the

distributary and controls the supply entering the distributary. A cross regulator is provided

41

on the main canal at the down stream of the off-take to head up the water level and to enable

the off-taking channel to draw the required supply.

Functions of distributary head regulators :

(1) These regulate orcontrol the supplies to the off-taking canal.

(2) To control silt entry into the off-take canal.

(3) To serve as a meter for measuring discharge.

Functions of cross regulators :

(1) To effectively control the entire canal irrigation system.

(2) When the water level in the main channel is low, it helps is heading up water on the

up stream and to feed the off-take channels to their full demand in rotation.

Falls :

Irrigation canals are constructed with some permissible bed slopes so that there is no

silting or scouring in the canal bed. But it is not always possible to run the canal at the

desired bed slope throughout the alignment due to the fluctuating nature of the country slope.

Generally the slope of the natural ground surface is not uniform through the

alignment. Sometimes the ground surface may be steep and sometimes it may be very

irregular with abrupt change of grade.

In this case “ a vertical drop is constructed across a canal to lower down its water

level and destroy the surplus energy liberated from the falling water which may otherwise

scour the bed and banks of the canal. This is done to avoid unnecessary huge earth work in

filling. Such vertical drops are known as Canal falls or Falls simply.”

Types of Falls :

The followings are the different types of canal falls.

(I) Ogee fall : In this type of falls, an ogee curve ( a combination of convex and

concave curve ) is provided for carrying the canal water from higher level to

lower level. This fall is recommended when the natural ground surface suddenly

changes to a steeper slope along the alignment of the canal. The fall consists of a

concrete vertical wall and concrete bed.

42

(fig.4 Ogee fall)

(II) Rapid fall : The Rapid fall is suitable when the slope of the natural ground

surface is even and long. It consists of a long slopping glacis with longitudinal

slope which varies 1 in vertical to 10 – 20 in horizontal. Curtain walls are

provided on the upstream and downstream side of the slopping glacis. The sloping

bed is provided with rubble masonry. The masonry surface is finishes with rich

cement mortar (1:2).

(Fig.5 Rapid Fall)

(III) Stepped fall : Stepped fall consists of a series of vertical drops in the form of

steps. This fall is suitable in places where the sloping ground is very long and

requires long glacis to connect the higher bed level with lower bed level. This fall

is practically a modification of the rapid fall. The sloping glacis is divided into a

number of drops so that the following water may not cause any dmage to the canal

bed. Brick walls are provided at each of the drops.

43

(Fig.6 Stepped Fall)

(IV) Trapezoidal North Fall :In this type of fall a body wall is constructed acroos the

canal. The body wall consists of several trapezoidal notches between the side piers

and the intermediate pier or piers. The sills of the notches are kept at the upstream

bed level of the canal.

(Fig.7 Trapezoidal notch fall)

(V) Glacis type fall :The glacis type fall utilised the standing wave phenomenon for

dissipation of energy. The glacis fall may be straight glacis or parabolic glacis

type.

Energy dissipaters :

The water flowing over the spillway acquires a lot of kinetic energy by the time it

reaches near the toe of the spillway. The arrangement is made to dissipate the huge kinetic

energy and the velocity of water is reduced on the downstream side near the toe of the dam.

This arrangement is known as energy dissipaters.

44

Canal Outlets :-

An outlet is a small structure which admits water from the distributing channel to a

water course or field channel. Thus, an outlet is a sort of head regulator for the field channel

delivering water to the irrigation fields.

Types of Outlets :-

Outlets may be classified as 3 types :

(1) Non modular outlet

(2) Semi- module or Flexible Module

(3) Rigid module.

1) Non modular outlet :-A non modular outlet is the one in which the discharge

depends upon the difference in level between the water levels in the distributing

channel and water course. The discharge through such an outlet varies in wide limits

with the fluctuations of the water levels in the distributing and field channels. The

common examples under this category are : Submerged pipe outlet, masonry sluice

and Orifices.

2) Semi module or Flexible module :- A flexible outlet or Semi module outlets the one

in which the discharge is affected by the fluctuations in the water level of the

discharging channel while the fluctuations in the water levels of the field channel do

not have any effect on its discharge.

Example:- Pipe Outlet, Kennedy’s gauge outlet, Pipe cum open flume outlet etc.

3) Rigid Module :- A rigid module is the one which maintains constant discharge,

within limits, irrespective of the fluctuations in water levels in the distributing channel

or field channel. Example : Gibb’s Rigid module.

CANAL ESCAPES :-

Canal escapes is defined as an channel meant for the removal of surplus or excess

water from the canal into nearby drainage. The function served by canal escape are :

(i) Safety valve to protect the canal against possible damage by flooding.

(ii) Emptying of the canal reach, below the escape, for silt or weed removal, repairs

and maintenance.

(iii) Periodical flushing off the silt prone head of a canal through the escape.

45

(Fig.8 Canal escape)

Depending upon the purpose, there can be 3 types of escapes such as :

a) Canal scouring escapes

b) Surplus escapes

c) Tail escapes

Canal scouring escapes :- The scouring escape is constructed for the purpose of scouring off

excess silt from time to time. Escapes are also constructed to dispose off excess supplies of

the parent channel. Excess supplies in the canal take place either during heavy rains or due to

the closure of canal outlet by the farmers. In that case, the escapes save the down stream

section of the canal from overflow of banks.

(Fig.9 Scouring Escape)

Surplus escape :- A canal surplus escape may be weir type, with the crest of weir wall at

F.S.L. of parent bed level.

46

Tail escape :- A tail escape is required F.S.L. at tail end. The structure is weir type with its

crest level at the required F.S.L. of canal at its tail end.

47

CHAPTER-7

CROSS DRAINAGE WORKS

A Cross drainage works is a structure carrying the discharge from a natural stream

across a Canal intercepting the stream.

OR

Canal comes across obstruction like rivers, natural drains, and other canals. The various

types of structure that ate built to carry the canal water across the above mentioned

obstructions or vice versa are called cross drainage works. � There are many different factors involved in selection of a specific type of cross drainage

works and in selection of a suitable site for cross drainage works. It is generally very

costly item & should be avoided by � Diverting one stream into another. � Changing the alignment of the canal, so that it crosses below the junction of two

streams.

NECESSITY OF CROSS DRAINAGE WORKS The following factors justify the necessity of cross drainage works. (a) At the crossing point, the water of the canal and the drainage get intermixed, So for

the smooth running of the canal with its design discharge, the cross drainage works

are required. (b) The site condition of the crossing point may be such that without any suitable

structure, the water of the canal and drainage cannot be diverted to their natural

directions. So, the cross drainage works must be provided to maintain their natural

direction of flow.

(c) The water shed canals do not cross natural drainage. But in actual orientation of the

canal network, this ideal condition may not be available and the obstacles like natural

drainages may be present across the canal. So, the cross- drainage works must be

provided for running the irrigation system.

48

TYPES OF CROSS- DRAINAGE WORKS

The drainage water intercepting the canal can be disposed of in either of the following

ways. (1) By passing the canal over the drainage. The structures that fall under this type are:-

(a) An Aqueduct.

(b) Syphon aqueduct. (2) By Passing the canal below the drainage. The structures that fall under this type are :

(a) Super passage

(b) Canal Syphon or syphon super passage. (3) By passing the drain through the canal, so that the canal water and drainage water are

allowed to intermingle with each other.

Following are the structures under this type of cross- drainage works:

(a) Level crossing.

(b) Inlet and outlet.

PROPER SITE FOR DAINAGE CROSSING The site selected for the cross. Drainage works should have the following main

characteristics. (1) It should be such that it requires minimum disturbance regarding the approach and tail

reaches of the drainage channel. (2) Suitable foundation soil should be available at reasonable depth. (3) Sufficient headway is available for the super structure of the aqueduct over the H.F.L.

of the natural stream. (4) Suitable existing topography, geological and hydraulic conditions for cross drainage

works at reasonable costs.

49

AQUEDUCT

The hydraulic structure in which the irrigation canal is taken over the drainage is known as

an aqueduct.

When the HFL of the drain is sufficiently be

structure is known as aqueduct. In this type of work, the canal water is taken across the

drainage in a trough supported an piers. An aqueduct is just like a bridge except that instead

of carrying a road or a railway, it carries a canal on its top. The advantage of such

arrangement is that the canal, running perennially, is above the ground and is open to

inspection.

An aqueduct is provided when sufficient level difference is available between the

canal and natural drainage, and canal bed level is sufficiently higher than the torrent level.

Generally the canal is in the shape of a rectangular trough and sometimes may be

trapezoidal section, which is constructed with R.C.C. The section of the trough is designed as

per the full supply level of the canal. The height & section of piers are designed according to

the highest flood level and velocity of flow of the drainage. The piers constructed may be

R.C.C., stone masonry or brick masonry. According to the availability

type of foundation provided. The bed & banks of drainage is protected by boulder pitching.

In case of the syphon aqueduct, the HFL of the drain is much higher above the canal

bed, and water runs under syphonic action through the aqueduct barrels or tunnels. Here the

sloping apron provided on both sides of the crossing. The apron may be constructed by

cement concert or stone pitching. The section of the drainage below the canal trough is

constructed with P.C.C. in the form of tunnel or barrels. This tunnel acts as a syphon. Cut

50

he hydraulic structure in which the irrigation canal is taken over the drainage is known as

OR

When the HFL of the drain is sufficiently below the bottom under gravity, such type of



way, it carries a canal on its top. The advantage of such



l drainage, and canal bed level is sufficiently higher than the torrent level.





R.C.C., stone masonry or brick masonry. According to the availability of soil, the depth &


SYPHON AQUEDUCT


s under syphonic action through the aqueduct barrels or tunnels. Here the



ted with P.C.C. in the form of tunnel or barrels. This tunnel acts as a syphon. Cut

he hydraulic structure in which the irrigation canal is taken over the drainage is known as

low the bottom under gravity, such type of



way, it carries a canal on its top. The advantage of such



l drainage, and canal bed level is sufficiently higher than the torrent level.





of soil, the depth &



s under syphonic action through the aqueduct barrels or tunnels. Here the



ted with P.C.C. in the form of tunnel or barrels. This tunnel acts as a syphon. Cut-off

walls are provided on both sides of the apron to prevent scouring diring heavy flood. Also

boulder pitching should be provided on the u/s and d/s of the cut

The hydraulic structure in which the drainage is passing over the irrigation canal is

known as super passage. It is reverse of an aqueduct. A super passage is similar to an

aqueduct, except in this case the drain

The FSL of the canal is lower than the underside of the trough carrying drainage

water. Thus the canal water runs under the gravity. The drainage is taken through a

rectangular or trapezoidal trough of channel which is constructed on t

piers. The section of the drainage trough depends on the high flood discharge. A free board of

about 1.5 m. should be provided for safety. The trough should be constructed of R.C.C. The

bed & banks of the canal below the drainage troug

or lining with concrete slabs.

SYPHON SUPER PASSAGE/ CANAL SYPHON/ SYPHON

51


boulder pitching should be provided on the u/s and d/s of the cut-off wall.

SUPER PASSAGE



aqueduct, except in this case the drain is over the canal.



rectangular or trapezoidal trough of channel which is constructed on the deck supported by



bed & banks of the canal below the drainage trough should be protected by boulder pitching







he deck supported by



h should be protected by boulder pitching


If the FSL of the canal is sufficiently above the bed level of the drainage trough, so that the

canal flows under syphonic action unde

a siphon super passage.

This structure is reverse of an syphon aqueduct. The section of the trough is designed

according to high flood discharge. The canal bed is lowered and a ramp is provided at th

entry & exit, so that the trouble of silting is minimized. The sloping apron may be

constructed with stone pitching or concert slabs. The section of the canal below the ttough is

constructed with cement concrete in the form of tunnel ehich acts as siphon

provided on u/s & d/s of the sloping apron to minimize scouring affect during high flood.

In this type of cross drainage work, the canal water and drain water are allowed to

intermingle with each other. A level crossing

huge drainage (Such as a stream or a river) approach each other practically at the same level.

In this type of work, the drainage water is passed into the canal & then taken out at

the opposite bank. The work consists of

I. Construction of crest, with its top at the FSL of the canal, at the u/s junction

with the canal.

II. Provision of the head regulator across the drainage at its d/s junction with the

canal.

III. A cross regulator across the cana A regulator at the end of the incoming canal is also sometimes required.

When the drainage does not carry any water, its regulator is closed while the cross

regulator of the canal is kept open so that the canal f

52

f the FSL of the canal is sufficiently above the bed level of the drainage trough, so that the

canal flows under syphonic action under the trough, the structure is known as canal syphon or


according to high flood discharge. The canal bed is lowered and a ramp is provided at th



constructed with cement concrete in the form of tunnel ehich acts as siphon. Cut


LEVEL CROSSING


intermingle with each other. A level crossing is generally provided when a large canal and



pposite bank. The work consists of

Construction of crest, with its top at the FSL of the canal, at the u/s junction

Provision of the head regulator across the drainage at its d/s junction with the

A cross regulator across the canal at its d/s junction with the drainage.

A regulator at the end of the incoming canal is also sometimes required.

When the drainage does not carry any water, its regulator is closed while the cross

regulator of the canal is kept open so that the canal flows without any interruption. During

f the FSL of the canal is sufficiently above the bed level of the drainage trough, so that the

r the trough, the structure is known as canal syphon or


according to high flood discharge. The canal bed is lowered and a ramp is provided at the



. Cut-off walls are



is generally provided when a large canal and



Construction of crest, with its top at the FSL of the canal, at the u/s junction

Provision of the head regulator across the drainage at its d/s junction with the

l at its d/s junction with the drainage.

When the drainage does not carry any water, its regulator is closed while the cross-

lows without any interruption. During

the floods, however, the drainage regulator is opened so that the flood discharge, after

spilling over the crest & mixing with the canal water, passes through it to the downstream of

the drainage.

In Case of crossing of a small irrigation channel with a small drainage, no hydraulic

structure is constructed, because, the discharged of the drainage and the channel are

practically low and these can be easily tackled by easy sy

arrangement. In this system an inlet is provided in the channel bank simply by open cut and

the drainage water is allowed to join the channel. Then at a suitable point on the downstream

side of the channel an outlet is provided b

is allowed to flow through a leading channel towards the original course of the drainage. At

the points of inlet the bed and banks of the drainage are protected by stone pitching. The bed

and banks of the irrigation channel between inlet and outlet points should also be protected

by stone pitching.

SELECTION OF SUITABLE TYPE OF CROSS

According to the relative bed levels of the canal and the river or drainage, the types

of cross drainage works are generally selected. However, in actual field, such ideal

conditions may not be available and the choice would then depends on following points: (a) The crossing should be at right angles to each other. (b) Availability of funds. (c) Suitability of soil for embankment. (d) Position of water table and availability of dewatering equipments.

53



INLET & OUTLET



practically low and these can be easily tackled by easy system like inlet and outlet



side of the channel an outlet is provided by open cut and the water from the irrigation channel



e irrigation channel between inlet and outlet points should also be protected

SELECTION OF SUITABLE TYPE OF CROSS- DRAINAGE WORKS


works are generally selected. However, in actual field, such ideal

conditions may not be available and the choice would then depends on following points:

The crossing should be at right angles to each other.

l for embankment.

Position of water table and availability of dewatering equipments.





stem like inlet and outlet



y open cut and the water from the irrigation channel



e irrigation channel between inlet and outlet points should also be protected

DRAINAGE WORKS


works are generally selected. However, in actual field, such ideal

conditions may not be available and the choice would then depends on following points:-

54

(e) Well defined c/s of the canal or river or drainage should be available.

(1) Availability of suitable foundation:-

For the construction of cross drainage works suitable foundation is required. By

boring test, if suitable foundation is not available, then the type cross drainage works

should be selected according to site condition. (2) Economical Consideration:-

The cost of construction of cross drainage works should be justified with respect to

the project cost and overall benefits of the project. So, the type of works should be

selected considering the economical point of view. (3) Discharge of the Drainage:-

Practically, the discharge of the drainage is very uncertain in rainy season. So, the

structure should be carefully selected so that it may not be destroyed due to

unexpected heavy discharge of the river or drainage. (4) Construction Problems:-

Different types of constructional problems may arise at the site such as sub-soil water,

construction materials, communication, availability of land, etc. So, the type of works

should be selected according to the site condition.

55

CHAPTER-8

DAM

8.1 INTRODUCTION

A dam is a hydraulic structure of fairly impervious material built across a river

to create a reservoir on its upstream side for impounding water for various purposes.

It is suitable in hilly region where a deep gorge section is available for the strange

reservoir. These purposes may be Irrigation, Hydro-power, Water-supply, Flood

Control, Navigation, Fishing and Recreation. Dams may be built to meet the one of

the above purposes or they may be constructed fulfilling more than one. As such, it

can be classified as: Single-purpose and Multipurpose Dam.

The dam is meant for serving multipurpose functions such as,

(a) Irrigation,(b)Hydroelectric power generation, (c)Flood control, (d)Water supply,

(e) Fishery, (f) Recreation.

Weir and Barrage are also impervious barriers across the river. Which are

suitable in plain terrain but not in hilly region. The purpose of weir is only to raise the

water level to some desired height and the purpose of barrage is to adjust the water

level at different levels when required. These to hydraulic structures are suitable for

irrigation only.

DIFFEREENT PARTS & TEREMELOGY OF DAMS:-

� Crest: The top of the dam structure. These may in some cases be used for

providing a roadway or walkway over the dam.

� Parapet walls: Low Protective walls on either side of the roadway or walkway on

the crest.

� Heel: Portion of structure in contact with ground or river-bed at upstream side.

� Toe: Portion of structure in contact with ground or river-bed at downstream side.

� Spillway: It is the arrangement made (kind of passage) near the top of structure

for the passage of surplus/ excessive water from the reservoir.

� Abutments: The valley slopes on either side of the dam wall to which the left &

right end of dam are fixed to.

� Gallery: Level or gently sloping tunnel like passage (small room like space) at

transverse or longitudinal within the dam with drain on floor for seepage water.

These are generally provided for having space for drilling grout holes and

drainage holes. These may also be used to accommodate the instrumentation for

studying the performance of dam.

� Sluice way: Opening in the structure near the base, provided to clear the silt

accumulation in the reservoir.

o Illustration of dam-parts in a typical cross section

� Free board: The space between the highest level of water in the reservoir and the

top of the structure.

� Dead Storage level: Level of permanent storage below which the water will not

be withdrawn.

� Diversion Tunnel: Tunnel constructed to divert or change the directi

to bypass the dam construction site. The hydraulic structures are built while the

river flows through the diversion tunnel.

SELECTION OF SITE FOR DAM

While selecting the site for a dam, the following points should be considered.

� Good rocky foundation should be available at the dam site. The nature of the

foundation soil should be examined by suitable method of soil exploration.

� The river valley should be narrow and well defined so that the length of the dam

may be short as far as possible.

� Site should be in deep gorge section of the valley so that large capacity storage

can be formed with minimum surface area and minimum length of dam.

� Valuable property and valuable land should not be submerged due to the

construction of dam.

o The proposed

sediment. If unavoidable, the sources of sediments should be located and

necessary measures should be recommended to arrest the sediment.

� The site should be easily accessible by road or railway f

construction materials, equipment’s, etc.

� The construction materials should be available in the vicinity of the dam site.

56

: Opening in the structure near the base, provided to clear the silt

accumulation in the reservoir.

parts in a typical cross section (click the image to view it clearly)

: The space between the highest level of water in the reservoir and the

: Level of permanent storage below which the water will not

: Tunnel constructed to divert or change the directi


river flows through the diversion tunnel.

SELECTION OF SITE FOR DAM


oundation should be available at the dam site. The nature of the


The river valley should be narrow and well defined so that the length of the dam

may be short as far as possible.

Site should be in deep gorge section of the valley so that large capacity storage


Valuable property and valuable land should not be submerged due to the

The proposed river or its tributaries should not carry large quantity of



The site should be easily accessible by road or railway for the transport of

construction materials, equipment’s, etc.

The construction materials should be available in the vicinity of the dam site.

: Opening in the structure near the base, provided to clear the silt

to view it clearly)

: The space between the highest level of water in the reservoir and the

: Level of permanent storage below which the water will not

: Tunnel constructed to divert or change the direction of water



oundation should be available at the dam site. The nature of the


The river valley should be narrow and well defined so that the length of the dam

Site should be in deep gorge section of the valley so that large capacity storage


Valuable property and valuable land should not be submerged due to the

river or its tributaries should not carry large quantity of



or the transport of

The construction materials should be available in the vicinity of the dam site.

57

� Sufficient space should be available near the site for the construction of labour

colony, godowns and staff quarters for the personnel associated with the

constructional activities.

� The basin should be free from cracks, fissures, etc. to avoid percolation loss. It is

done by physical verification and other observations, If unavoidable, the area

should be located and necessary measures should be recommended to make the

area leak-proof.

� From the rainfall records in the catchment area or empirical formulae the

maximum discharge of the river should be ascertained whether the required

quantity of water shall be available or not.

INVESTIGATION WORKS FOR DAM SITE

The following investigation works should be done before final selection of dam site

and the preparation of the project report.

1. Preliminary Survey: the preliminary survey involves the following steps.

(a) Reconnaissance survey : the reconnaissance survey should be conducted for

the dam site and surrounding area to gather information regarding the natural

features of the area, nature of dam site, location of labour colony and staff

quarters, stack yard, dodowns, etc. the nature of the land and the localities in

the basin area should also be recorded. And index map should be prepared.

(b) Topographical survey: A topographical map is to be prepared for the

proposed project area by traverse surveying. The traverse survey may be

conducted any suitable method depending on the nature of the area.

(c) Contour Survey: A contour map should be prepared for the basin area to

determine the capacity of the reservoir.

(d) Contour Survey: longitudinal leveling and cross-sectional leveling should be

done at the dam site at least one km upstream and downstream of the proposed

centerline of the dam. This is done to select the most suitable dam site.

2. Geological Survey: the geological survey involves the following steps

a. Soil Survey: To work the nature of the foundation at the dam site. Soil

exploration should be done by suitable method. The sub-soil formation should

be thoroughly studied to determine the type of foundation for the dam.

b. Study of formation in basin area: Soil exploration should be done at

different spot in the basin area to ascertain the nature of sub-soil. This is done

to calculate the probable percolation loss.

c. Study of source of Sediment: The sources of sediments carried by the river

or its tributaries should be studied and located. If slips or areas of loose soil

58

with mica particles are found, then the stabilization of those areas should be

done.

3. Hydrological Survey: It involves the following steps:

a. Gauge and discharge site: The gauge and discharge stations should be

established near the dam site to record the discharge of the river throughout

the year.

b. Site analysis: In rainy season the river carries heavy silt or sediment. The

analysis of the silt should be carried out throughout the season for some

specific period to determine grade of silt. This is done to ascertain the possible

sedimentation in the reservoir and thus suitable methods can be employed to

reduce the sedimentation.

4. Communication Survey: The route survey for the possible communication of

the dam site the nearest highway or railway station should be done. It involves the

preparation of longitudinal section and cross-sections along the proposed

alignment. It is done to estimate the cost of construction of this connecting road or

railway lie. The possible route for telephone communication and electrical

connections should also be located.

5. Construction Materials Survey: The availability of construction materials like

stone, sand, etc. should be located in the topographical map of the concerned

district or state. The possible route for carrying these materials should also be

located in the map.

6. Compensation Report: A detailed report should be prepared for the

compensation which is likely to be paid by the government during the

implementation of the project. This will include the dam site, area of labour

colony and staff quarters, area required for stack yards and godowns, valuable

lands and properties that may be submerged by the reservoir, etc.

7. Project Report: The project involves the following steps:

a. Design and estimate of dam and other allied structures.

b. Detailed drawings of dam section with foundation and other buildings or

structures.

c. Detailed estimate for the road or railway communication.

d. Comprehensive report for compensation.

e. The project is forwarded to the higher authority with recommendation for

approval.

f. The project is forward to the higher authority with recommendation for

approval.

59

CLASSIFICATION OF DAMS:

Dams can be classified in number of ways. But most usual ways of classification i.e.

types of dams are mentioned below:

Based on the functions of dams, it can be classified as follows:

1. Storage dams: They are constructed to store water during the rainy season when

there is a large flow in the river. Many small dams impound the spring runoff for

later use in dry summers. Storage dams may also provide a water supply, or

improved habitat for fish and wildlife. They may store water for hydroelectric

power generation, irrigation or for a flood control project. Storage dams are the

most common type of dams and in general the dam means a storage dam unless

qualified otherwise.

2. Diversion dams: A diversion dam is constructed for the purpose of diverting

water of the river into an off-taking canal (or a conduit). They provide sufficient

pressure for pushing water into ditches, canals, or other conveyance systems. Such

shorter dams are used for irrigation, and for diversion from a stream to a distant

storage reservoir. It is usually of low height and has a small storage reservoir on

its upstream. The diversion dam is a sort of storage weir which also diverts water

and has a small storage. Sometimes, the terms weirs and diversion dams are used

synonymously.

3. Detention dams: Detention dams are constructed for flood control. A detention

dam retards the flow in the river on its downstream during floods by storing some

flood water. Thus the effect of sudden floods is reduced to some extent. The water

retained in the reservoir is later released gradually at a controlled rate according to

the carrying capacity of the channel downstream of the detention dam. Thus the

area downstream of the dam is protected against flood.

4. Debris dams: A debris dam is constructed to retain debris such as sand, gravel,

and drift wood flowing in the river with water. The water after passing over a

debris dam is relatively clear.

5. Coffer dams: It is an enclosure constructed around the construction site to

exclude water so that the construction can be done in dry. A coffer dam is thus a

temporary dam constructed for facilitating construction. These structure are

usually constructed on the upstream of the main dam to divert water into a

diversion tunnel (or channel) during the construction of the dam. When the flow in

the river during construction of hydraulic structures is not much, the site is usually

enclosed by the coffer dam and pumped dry. Sometimes a coffer dam on the

downstream of the dam is also required.

Based on structure and design, dams can be classified as follows:

1. Gravity Dams: A gravity dam is a massive sized dam fabricated from concret

stone masonry. They are designed to hold back large volumes of water. By using

concrete, the weight of the dam is actually able to resist the horizontal thrust of water

pushing against it. This is why it is called a gravity dam. Gravity essentially ho

dam down to the ground, stopping water from toppling it over.

a. b. Types of dam

i. Gravity dams are well suited forblocking rivers in wide valleys or

narrow gorge ways. Since gravity dams must rely on their own weight

to hold back water, it is necessary

foundation ofbedrock.

Examples of Gravity dam: Grand Coulee Dam (USA), Nagarjuna

Sagar (India) and Itaipu

is the largest in the world).

2. Earth Dams: An earth dam is made of earth (

successive layers of earth, using the most impervious materials to form a core and

placing more permeable substances on the upstream and downstream sides. A facing

of crushed stone prevents erosion by wind or rain, and an am

concrete, protects against catastrophic washout should the water overtop the dam.

Earth dam resists the forces exerted upon it mainly due to shear strength of the soil.

Although the weight of the structure also helps in resisting t

behavior of an earth dam is entirely different from that of a gravity dam. The earth

dams are usually built in wide valleys having flat slopes at flanks (abutments).The

foundation requirements are less stringent than those of grav

can be built at the sites where the foundations are less strong. They can be built on all

types of foundations. However, the height of the dam will depend upon the strength of

the foundation material.

Examples of earthfill dam: Ron

60

Based on structure and design, dams can be classified as follows:

: A gravity dam is a massive sized dam fabricated from concret



pushing against it. This is why it is called a gravity dam. Gravity essentially ho

dam down to the ground, stopping water from toppling it over.

Gravity dams are well suited forblocking rivers in wide valleys or


to hold back water, it is necessary that they are built on a solid



Sagar (India) and Itaipu Dam (It lies Between Brazil and Paraguay and

is the largest in the world).

: An earth dam is made of earth (or soil) built up by compacting



of crushed stone prevents erosion by wind or rain, and an ample spillway, usually of



Although the weight of the structure also helps in resisting the forces, the structural



foundation requirements are less stringent than those of gravity dams, and hence they




Examples of earthfill dam: Rongunsky dam (Russia) and New Cornelia Dam (USA).

: A gravity dam is a massive sized dam fabricated from concrete or



pushing against it. This is why it is called a gravity dam. Gravity essentially holds the

Gravity dams are well suited forblocking rivers in wide valleys or


that they are built on a solid



Dam (It lies Between Brazil and Paraguay and

or soil) built up by compacting



ple spillway, usually of



he forces, the structural



ity dams, and hence they




gunsky dam (Russia) and New Cornelia Dam (USA).

61

3. Rockfill Dams: A rockfill dam is built of rock fragments and boulders of large size.

An impervious membrane is placed on the rockfill on the upstream side to reduce the

seepage through the dam. The membrane is usually made of cement concrete or

asphaltic concrete.

a. b. Mohale Dam, Lesotho, Africa

In early rockfill dams, steel and timber membrane were also used, but now

they are obsolete. A dry rubble cushion is placed between the rockfill and the

membrane for the distribution of water load and for providing a support to the

membrane. Sometimes, the rockfill dams have an impervious earth core in the middle

to check the seepage instead of an impervious upstream membrane. The earth core is

placed against a dumped rockfill. It is necessary to provide adequate filters between

the earth core and the rockfill on the upstream and downstream sides of the core so

that the soil particles are not carried by water and piping does not occur. The side

slopes of rockfill are usually kept equal to the angle of repose of rock, which is

usually taken as 1.4:1 (or 1.3:1). Rockfill dams require foundation stronger than those

for earth dams.

Examples of rockfill dam: Mica Dam (Canada) and Chicoasen Dam (Mexico).

4. Arch Dams: An arch dam is curved in plan, with its convexity towards the upstream

side. They transfer the water pressure and other forces mainly to the abutments by

arch action.

Hoover dam (USA)

62

An arch dam is quite suitable for narrow canyons with strong flanks which are

capable of resisting the thrust produced by the arch action. The section of an arch dam

is approximately triangular like a gravity dam but the section is comparatively

thinner. The arch dam may have a single curvature or double curvature in the vertical

plane. Generally, the arch dams of double curvature are more economical and are

used in practice.

Examples of Arch dam: Hoover Dam (USA) and Idukki Dam (India).

5. Buttress Dams: Buttress dams are of three types : (i) Deck type, (ii) Multiple-arch

type, and (iii) Massive-head type. A deck type buttress dam consists of a sloping deck

supported by buttresses. Buttresses are triangular concrete walls which transmit the

water pressure from the deck slab to the foundation. Buttresses are compression

members. Buttresses are typically spaced across the dam site every 6 to 30 metre,

depending upon the size and design of the dam. Buttress dams are sometimes called

hollow dams because the buttresses do not form a solid wall stretching across a river

valley.The deck is usually a reinforced concrete slab supported between the

buttresses, which are usually equally spaced

.

In a multiple-arch type buttress dam the deck slab is replaced by horizontal arches

supported by buttresses. The arches are usually of small span and made of concrete. In

a massive-head type buttress dam, there is no deck slab. Instead of the deck, the

upstream edges of the buttresses are flared to form massive heads which span the

distance between the buttresses. The buttress dams require less concrete than gravity

dams. But they are not necessarily cheaper than the gravity dams because of extra cost

of form work, reinforcement and more skilled labor. The foundation requirements of a

buttress are usually less stringent than those in a gravity dam.

Examples of Buttress type: Bartlett dam (USA) and The Daniel-Johnson Dam

(Canada).

6. Steel Dams: Dams: A steel dam consists of a steel framework, with a steel skin plate

on its upstream face. Steel dams are generally of two types: (i) Direct-strutted, and (ii)

Cantilever type . In direct strutted steel dams, the water pressure is transmitted

directly to the foundation through inclined struts. In a cantilever type steel dam, there

is a bent supporting the upper part of the deck, which is formed into a cantilever truss.

This arrangement introduces a tensile force in the deck girder which can be taken care

of by anchoring it into the foundation at the upstream toe. Hovey suggested that

tension at the upstream toe may be reduced by flattening the slopes of the lower struts

in the bent.

However, it would require heavier sections struts for Another alternative to reduce

tension is to frame together the entire bent rigidly so that the moment due to the

weight of the water on the lower part of the deck is utilized to o

induced in the cantilever. This arrangement would, however, require bracing and this

will increase the cost. These are quite costly and are subjected to corrosion. These

dams are almost obsolete. Steel dams are sometimes used as temporary

during the construction of the permanent one. Steel coffer dams are supplemented

with timber or earthfill on the inner side to make them water tight. The area between

the coffer dams is dewatered so that the construction may be done in dry for

permanent dam.

Examples of Steel type: Redridge Steel Dam (USA) and Ashfork

Dam (USA).

7. Timber Dams: Main load

wood, primarily coniferous varieties such as pine and fir. Timber dams

small heads (2-4 m or, rarely, 4

of the apron they are divided into pile, crib, pile

63



.



weight of the water on the lower part of the deck is utilized to offset the moment



dams are almost obsolete. Steel dams are sometimes used as temporary



the coffer dams is dewatered so that the construction may be done in dry for

permanent dam.

Examples of Steel type: Redridge Steel Dam (USA) and Ashfork-Bainbridge Steel

: Main load-carrying structural elements of timber dam are made of

wood, primarily coniferous varieties such as pine and fir. Timber dams

4 m or, rarely, 4-8 m) and usually have sluices; according to the design

of the apron they are divided into pile, crib, pile-crib, and buttressed dams.





ffset the moment



dams are almost obsolete. Steel dams are sometimes used as temporary coffer dams



the coffer dams is dewatered so that the construction may be done in dry for the

permanent dam.

Bainbridge Steel

carrying structural elements of timber dam are made of

are made for

8 m) and usually have sluices; according to the design

crib, and buttressed dams.

64

Timber dam

The openings of timber dams are restricted by abutments; where the sluice is very

long it is divided into several openings by intermediate supports: piers, buttresses, and

posts. The openings are covered by wooden shields, usually several in a row one

above the other. Simple hoists—permanent or mobile winches—are used to raise and

lower the shields.

8. Rubber Dams: A symbol of sophistication and simple and efficient design, this most

recent type of dam uses huge cylindrical shells made of special synthetic rubber and

inflated by either compressed air or pressurized water. Rubber dams offer ease of

construction, operation and decommissioning in tight schedules.

a. b. These can be deflated when pressure is released and hence, even the crest level

can be controlled to some extent. Surplus waters would simply overflow the

inflated shell. They need extreme care in design and erection and are limited to

small projects.

EARTHEN DAM

Earthen dams are constructed purely by earth work in trapezoidal section.

These are most economical and suitable for weak foundation. Earthen dams are

classified as follows:-

65

Based on Method of Construction

Rolled fill Dam:

In this method, the dam is constructed in successive layers of earth by

mechanical compaction. The selected soil is transported from borrow pits and laid on

the dam section, to layers of about 45 cm. The layers are thoroughly compacted by

rollers of recommended weight and type. When the compaction of one layer is fully

achieved, the next layer is laid and compacted in the usual way. The designed dam

section hence is completed layer by layer.

Hydraulic Fill Dam:

In this method, the dam section is constructed with the help of water.

Sufficient water is poured in the borrow pit and by plugging thoroughly, slurry is

formed. This slurry is transported to the dam site by pipe line and discharged near the

upstream and downstream faces of the dam. The coarser material gets deposited near

the face and the finer material move towards the centre and gets deposit there. Thus

the dam section is formed with faces of coarse material and central core is of

impervious materials like clay and silt. In this case, compaction is not necessary.

Semi-Hydraulic Fill Dam:

In this method the selected earth is transported from the borrowpit and

dumped within the section of the dam, as done in the case of rolled fill dam. While

dumping no water is used. But, after dumping the water jet is forced on the dumped

earth. Due to the action of water the finer materials move towards the centre of the

dam and an impervious core is formed with fine materials like clay. The outside body

is formed by coarse material, In this case also compaction is not necessary.

66

Homogeneous Type Dam:

This type of dam is constructed purely with earth in trapezoidal section having

the side slopes according to the angle of repose of the soil. The top width and height

deponents on the depth of water to be retained and the gradient of the seepage line.

The phreatic line (top level of seepage line) should pass well within the body of the

dam. This type of dam is completely pervious. The upstream face of the dam is

protected by stone pitching. Now-a- days, the earthen dam is modified by providing

horizontal drainage blanket or rock toe.

Zoned Type Dam:

This type of dam consists of several materials. The impervious core is made of puddle

clay and the outer previous shell is constructed with the mixture of earth, sand, gravel,

etc. the core is trapezoidal in section and its width depends on the seepage

characteristics of the soil mixture on the upstream side. The core is extended below

the both sides of the impervious core to control the seepage. The transition filter is

made of gravel and coarse sand. The upstream face of the dam is protected by stone

pitching.

Diaphragm Type Dam:

In this type of dam, a thin impervious core of diaphragm is provided which may

consist of puddle clay or cement concrete or bituminous concrete. The upstream and

downstream body of the dam is constructed with pervious shell which consists of the

mixture of soil, sand, gravel, etc. the thickness of the core is generally less than 3m. A

blanket of stones is provided on the toe of the dam for the drainage of the seepage

water without damaging the base of the dam. The upstream face is protected by stone

pitching. The side slope of the dam should be decided according to the angle of repose

of the soil mixture.

CAUSES OF FAILURE OF EARTHEN DAM

The failure of the earthen dam may be caused due to the reasons.

1. Hydraulic Failure : this type of failure may be caused by:

a. Overtopping: If the actual flood discharge is much is much more than the

estimated flood discharge or the fee board is kept insufficient or there is

settlement of the dam or the capacity of spill way is insufficient, then it results in

the overtopping of the dam. During the overtopping the crest of the dam may be

washed out and the dam may collapse.

b. Erosion: If the stone of the upstream side is insufficient, then the upstream face

may be damaged by erosion due to wave action. The downstream side also may be

damaged by tail water, rainwater, etc. The toe of the dam may also get damaged

by the water flowing through the spill ways.

67

c. Seepage Failure : this type of failure may be caused by:

d. Piping of undermining: Due to the continuous seepage flow through the body of

the dam and through the sub-soil below the dam, the downstream side gets eroded

or wshed out and a hollow pipe like groove is formed which extends gradually

towards the upstream through the base of the dam. This phenomenon is known as

piping or undermining. This effect weakens the dam and ultimately causes failure

of the dam.

e. Sloughing: the crumbling of the tow of the dam is known as sloughing. When the

reservoir runs full, for a longer time, the downstream base of the dam remains

saturated. Due to the force of the seepage water the toe of the dam goes on

crumbling gradually. Ultimately the base of the dam collapses.

f. Structural Failure : This type failure may be caused by

g. Sliding of the side slopes : Sometimes, it is found that the side slope of the dam

slides down to form some steeper slope. The dam goes on depressing gradually

and then overtopping occurs which leads to the failure of the dam.

h. Damage by burrowing animals: due to earthquake cracks may develop on the

body of the dam and the dam may eventually Collapse.

SOLID GRAVITY DAM

The solid gravity dam may be constructed with rubble masonry or concrete. The

rubble masonry is done according to the shape of the dam with rich cement mortar.

The upstream and downstream face are finished with rich cement mortar. Non-a-days,

concrete gravity dams are preferred, because they can be easily constructed by laying

concrete, layer by layer with construction joints. But good rocky foundation must be

available to bear the enormous weight of the dam. The distance between the heel and

toe is considered as the base width. It depends, on the height of the dam. Again, the

height depends on the nature of foundation. If good rocky foundation is available, the

height may be above 200 m. If hard foundation is not available, the height of the dam

should be limited to about 20m. The upstream and downstream base of dam is made

sloping. The horizontal trace (or line) passing through the upstream top edge is known

as axis of the dam or the base line. The layout of the dam is done corresponding to

this base line. Drainage gallery is provided at the base of the dam. Spill ways are

provided at the full reservoir level to allow the surplus water to flow to the

downstream. The solid gravity dam resists all the forces acting on it by its self-weight.

FORCES ACTING ON GRAVITY DAM.

1. Weight of the dam.

2. Water pressure

68

3. Uplift pressure.

4. Pressure due to earthquake

5. Ice pressure

6. Wave pressure

7. Silt Pressure

8. Wind Pressure

Following are the modes of failure of a Gravity Dam:

1.Overturning

2.Sliding

3. Compression or Crushing

4. Tension

SPILLWAYS:

Spillways are structures constructed to provide safe release of flood waters

from a dam to a downstream are, normally the river on which the dam has been

constructed.

Every reservoir has a certain capacity to store water. If the reservoir is full and

flood waters enter the same, the reservoir level will go up and may eventually result in

over-topping of the dam. To avoid this situation, the flood has to be passed to the

downstream and this is done by providing a spillway which draws water from the top

of the reservoir. A spillway can be a part of the dam or separate from it.

Spillways can be controlled or uncontrolled. A controlled spillway is provided

with gates which can be raised or lowered. Controlled spillways have certain

advantages as will be clear from the discussion that follows. When a reservoir is full,

its water level will be the same as the crest level of the spillway.

This is the normal reservoir level. If a flood enters the reservoir at this time,

the water level will start going up and simultaneously water will start flowing out

through the spillway. The rise in water level in the reservoir will continue for some

time and so will the discharge over the spillway. After reaching a maximum, the

69

reservoir level will come down and eventually come back to the normal reservoir

level.

The top of the dam will have to be higher than the maximum reservoir level

corresponding to the design flood for the spillway, while the effective storage

available is only up to the normal reservoir level. The storage available between the

maximum reservoir level and the normal reservoir level is called the surcharge storage

and is only a temporary storage in uncontrolled spillways. Thus for a given height of

the dam, part of the storage - the surcharge storage is not being utilized. In a

controlled spillway, water can be stored even above the spillway crest level by

keeping the gates closed. The gates can be opened when a flood has to be passed.

Parameters considered in Designing Spillways

Thus controlled spillways allow more storage for the same height of the dam. Many

parameters need consideration in designing a spillway. These include:

1. The inflow design flood hydro-graph

2. The type of spillway to be provided and its capacity

3. The hydraulic and structural design of various components and

4. The energy dissipation downstream of the spillway.

The topography, hydrology, hydraulics, geology and economic considerations all have

a bearing on these decisions. For a given inflow flood hydro graph, the maximum rise

in the reservoir level depends on the discharge characteristics of the spillway crest and

its size and can be obtained by flood routing. Trial with different sizes can then help

in getting the optimum combination.

Types of Spillways - Classification of Spillways

There are different types of spillways that can be provided depending on the

suitability of site and other parameters. Generally a spillway consists of a control

structure, a conveyance channel and a terminal structure, but the former two may be

combined in the same for certain types. The more common types are briefly described

below.

Ogee Spillway

The Ogee spillway is generally provided in rigid dams and forms a part of the main

dam itself if sufficient length is available. The crest of the spillway is shaped to

conform to the lower nappe of a water sheet flowing over an aerated sharp crested

weir.

Chute (Trough) Spillway

In this type of spillway, the water, after flowing over a short crest or other kind of

control structure, is carried by an open channel (called the "chute" or "trough") to the

70

downstream side of the river. The control structure is generally normal to the

conveyance channel. The channel is constructed in excavation with stable side slopes

and invariably lined. The flow through the channel is super-critical. The spillway can

be provided close to the dam or at a suitable saddle away from the dam where site

conditions permit.

Side Channel Spillway

Side channel spillways are located just upstream and to the side of the dam. The water

after flowing over a crest enters a side channel which is nearly parallel to the crest.

This is then carried by a chute to the downstream side. Sometimes a tunnel may be

used instead of a chute.

Shaft (Morning Glory or Glory hole) Spillway

This type of spillway utilizes a crest circular in plan, the flow over which is carried by

a vertical or sloping tunnel on to a horizontal tunnel nearly at the stream bed level and

eventually to the downstream side. The diversion tunnels constructed during the dam

construction can be used as the horizontal conduit in many cases.

Siphon Spillway

As the name indicates, this spillway works on the principle of a siphon. A hood

provided over a conventional spillway forms a conduit. With the rise in reservoir level

water starts flowing over the crest as in an "ogee" spillway. The flowing water

however, entrains air and once all the air in the crest area is removed, siphon action

starts. Under this condition, the discharge takes place at a much larger head. The

spillway thus has a larger discharging capacity. The inlet end of the hood is generally

kept below the reservoir level to prevent floating debris from entering the conduit.

This may cause the reservoir to be drawn down below the normal level before the

siphon action breaks and therefore arrangement for de-priming the siphon at the

normal reservoir level is provided.

71

CHAPTER-9

GROUND WATER AND ITS DEVELOPMENT

9.1 Occurrence of Ground Water: The rainfall that percolates below the ground surface, passes through the voids of the

rocks, and joins the watertable. These voids are generally inter-connected, permitting the

movement of the ground water. But in some rocks, they may be isolated, and thus, preventing

the movement of water between the interstices. Hence, it is evident that the mode of

occurrence of ground water depends largely upon the type of formation, and hence upon the

geology of the area.

In fact, all the materials of variable porosity (or interstices) near the upper portion of

the earth’s crust can be considered as a potential storage place for ground water, and hence

might be called as the ground water reservoir. The volume of water contained in the ground

water reservoir in any localized area, i.e. the water storage capacity of the ground water is

dependent upon (i) the porosity of the rocks; (ii) the rate at which water is added to it by

infiltration, transpiration, seepage to surface courses, and withdrawn by man.

Ground Water Yield(Quantity of Ground water):

The interstices present in the given formation get filled up with water during the

process of ground-water replenishment. If all these voids are completely filled with water,

then it is known as saturated formation. The water contained in these voids is drained by

digging wells under the action of ‘gravity-drainage’ (explained later. When these saturated

formations are drained under the action of ‘gravity drainage’, it is found that the volume of

water so drained is less than the volume of the void space as indicated by its porosity. This is

because of the fact, that the entire water contained in these voids cannot be drained out by

mere force of gravity. Some of the water is being retained by these interstices due to their

molecular attraction. The water so retained is known as pellicular water.

Specific Yield:

The volume of ground-water extracted by gravity-drainage from a saturated water

bearing material is known as the yield, and when it is expressed as ratio of the volume of the

total material drained, then it is known as specific field.

100dewateredor drained material theof volumeTotal

drainagegravity by obtained water of volume. ×=∴ yieldSp

72

1.4 Specific retention or Field Capacity:

On the other hand, the quantity of water retained by the material against the pull of

gravity is termed as specific retention or field capacity, and this is also expressed as

percentage of the total volume of the material drained.

100 drained material theof volumeTotal

drainagegravity against held water of volume×=capacityfieldortentionSpecificre

It is evident that the sum of the specific yield and specific retention is equal to its porosity.

1.5 Specific Retention of different Kinds of Formations:

As has been said earlier, the specific retention is the amount of the water held between

the grains due to molecular attraction. This film of water is thus held by molecular adhesion

on the walls of the interstices. Therefore, the amount of this water will depend upon the total

interstitial surface in the rock. If the total interstitial surface is more, the specific retention

will be more and vice versa.

Now, if the effective size of the grains decreases, the surface area between the

interstices will increase, leading to, more specific retention and less specific yield.

It, therefore, follows that, in fine soils like clay, the specific retention would be more,

and hence, such soils would result in very small specific yields.

The reverse is also true when the grain size increases; the interstitial surface area

reduces, and , therefore, sp. Retention reduces and hence sp. Yield increases. It, therefore,

follow that in large particle soils like coarse gravels, the specific retention would be small and

it would result in large specific yields.

This conclusion is very important from practical stand point, because it follows from

this that a water bearing formation of coarse gravel would supply large quantities of water to

wells, whereas, clay formations although saturated and of high porosity, would be of little

ably upon the type of neighboring formations.

Aquifers and Their Types:

A permeable stratum or a geological formation of permeable material, which is

capable of yielding appreciable quantities of ground water under gravity, is known as aquifer.

The term ‘appreciable quantity’ is relative, depending upon the availability of the ground

water. In the regions, where ground

materials containing very less quantities of water may be classified as Principal aquifers.

When an aquifer is obtained by a confined bed of impervious material, then this

confined bed of overburden is called as aquiclude, as shown in Fig. 9.1

The amount of water yielded by a well excavated through an aquifer, depends on

many factors, some of which, such as well diameter, are inherent in the well itself. But all

other things being equal, the permeability and the thickness of the aquifer are the m

important.

Aquifer very in depth, lateral extend, and thickness; but in general, all aquifer fall into

one of the two categories, i.e.,

1. Unconfined or Non-artesian aquifers; and

2. Confined or Artesian aquifer.

Unconfined Aquifer or Non-artesian aquifers:

The top most water bearing stratum having no confined impermeable over burden

(i.e., aquiclude) lying over it, is known as an unconfined aquifer or non

(Refer Fig. 9.2)

73


ppreciable quantities of ground water under gravity, is known as aquifer.


water. In the regions, where ground-water is available with great difficult, even fine



confined bed of overburden is called as aquiclude, as shown in Fig. 9.1

he amount of water yielded by a well excavated through an aquifer, depends on


other things being equal, the permeability and the thickness of the aquifer are the m


artesian aquifers; and

Confined or Artesian aquifer.

artesian aquifers:


(i.e., aquiclude) lying over it, is known as an unconfined aquifer or non-artesian aquifer


ppreciable quantities of ground water under gravity, is known as aquifer.


water is available with great difficult, even fine-grained



he amount of water yielded by a well excavated through an aquifer, depends on


other things being equal, the permeability and the thickness of the aquifer are the most



artesian aquifer

The ordinary gravity wells of 2 to 5 m diameter, which are con

from the top most water bearing strata, i.e., from the unconfined aquifers, are known as

unconfined or non-artesian wells. The water levels in these wells will be equal to the level of

the watertable. Such well are, therefore, also kn

Confined Aquifers or Artesian Aquifers:

When an aquifer is confined on its upper and under surface, by impervious rock

formations (i.e., aquicludes), and is also broadly inclined so as to expose the aquifer

somewhere to the catchments area at a higher level for the creation of sufficient dydraulic

head, it is called a confined aquifer or an artesian aquifer. A well excavated through such an

aquifer, yields water than often flows out automatically, under the hydrostatic press

may thus, even rise or gush out of surface for a reasonable height. However, where the

ground profile is high , the water may remain well below the ground level. The former type

of artesian wells, where after is gushing out automatically, are call

The level to which water will rise in an artesian well is determined by the highest

point on the aquifer, from where it is fed from

74

The ordinary gravity wells of 2 to 5 m diameter, which are constructed to gap water


artesian wells. The water levels in these wells will be equal to the level of

the watertable. Such well are, therefore, also known as wells or gravity wells.

Confined Aquifers or Artesian Aquifers:



catchments area at a higher level for the creation of sufficient dydraulic


aquifer, yields water than often flows out automatically, under the hydrostatic press



of artesian wells, where after is gushing out automatically, are called flowing wells.


point on the aquifer, from where it is fed from

structed to gap water


artesian wells. The water levels in these wells will be equal to the level of



catchments area at a higher level for the creation of sufficient dydraulic


aquifer, yields water than often flows out automatically, under the hydrostatic pressure, and



ed flowing wells.


75

The rains falling in the catchments (i.e., by discharge). However, the water will not

rise to this full height, because the friction of the water moving through the aquifer uses up

some of the energy.

The question whether it will be a flowing artesian well or a non-flowing artesian well

depends upon the topography of the area, and is not the inherent property of the artesian

aquifer. In fact, if the pressure surface lies above the ground surface, the well will be a

flowing artesian well, whereas, if the pressure surface is below the ground surface, the well

will be artesian but non-flowing, and will require a pump to bring water to the surface, as

shown in Fig.9.3. Such non-flowing artesian wells are sometimes called as sub-artesian wells.

Perched Aquifers:

Perched aquifer is a special case which is sometimes found to occur within an

unconfined aquifer.

If within the zone of saturation, an impervious deposit below a pervious deposit is

found to support a body of saturated materials, then this body of saturated materials which is

a kind of aquifer is known as perched aquifer. The top surface of the water held in the

perched aquifer is known as perched water table. This is shown in Fig. 9.4.

Wells

A water well is a hole usually vertical, excavated in the eared for brining ground

water to the surface. The wells may be classify into two types:

1. Open wells; and

2. Tube wells.

Open Wells or Dug Wells.

Smaller amount of ground water has been utilized from ancient times by open wells.

Open wells are generally open masonry wells having comparatively bigger diameters, and are

suitable for low discharges of the order of 18 cubic maters per hour (i.e. about 0.005 cumecs).

The diameter of than 20 m in depth. The walls of an open well may be built of precast

concrete rings or in brick or stone masonry, the thickness generally varies from 0.05 to 0.75

m, according to the depth of the well.

The yield of an open well is limited because such wells can be excavated only to a

limited depth where the ground water storage is also limited.

Moreover, in such a well the water, the water can be withdrawn only at the critical

velocity for the soil. Higher velocities cannot be permitted as that may lead to disturbance of

soil grains and consequent subsidence of well lining in the hollow so formed. The limit

placed

On velocity , therefore, also limits the maximum possible safe

One of the recent methods used to improve the yield of an open well is to put in a 8 to

10 cm diameter bore hole in the centre of the well, so as to tap the additional water from an

aquifer or from fissures in the rock. If a c

as to support the open masonry well, a bore hole can be made in its centre so as to reach the

76


limited depth where the ground water storage is also limited.


elocity for the soil. Higher velocities cannot be permitted as that may lead to disturbance of


On velocity , therefore, also limits the maximum possible safe dis-charge of an open well.



aquifer or from fissures in the rock. If a clay or kankar layer is available at a smaller depth so




elocity for the soil. Higher velocities cannot be permitted as that may lead to disturbance of


charge of an open well.



lay or kankar layer is available at a smaller depth so


sand strata. Such an arrangement will not only give a structural support to the open well but

will also considerably increase its yield. Depending upon the availability of such a provision,

the open wells may be classified into the following two types :

(a) Shallow wells; and

(b) Deep wells.

Shallow wells are those which rest in a pervious stratum and draw their suppli

the surrounding materials. On the other hand, a deep well is one which rests on an impervious

‘mota’ layer and draws its supply from the pervious formation lying below the mota layer,

through a bore hole made into the ‘mota’ layer, as shown in Fig

also sometimes known as “Matbarwa” or “Magasan”, referes to a layer of clay, cemented

sand,

kankar or other hard materials, which are often found lying a few metres below the

watertable in the sub-soil. The names are

the watertable. The main advantage of such a mota layer lies in giving structural support to

the open well resting on its surface. It is useful for unlined and partly lined wells, and is

indispensable for a heavy masonry well which would not remain stable under steady use

without such a support. The mota layer is generally found throughout the indo

These mote layer may either be continuous or may be localized, and are generally found in

different thicknesses and depths at different places.

77


siderably increase its yield. Depending upon the availability of such a provision,

the open wells may be classified into the following two types :

Shallow wells are those which rest in a pervious stratum and draw their suppli



through a bore hole made into the ‘mota’ layer, as shown in Fig. 4016. The term “Mota layer”



soil. The names are not applied to layers of hard material lying above



a heavy masonry well which would not remain stable under steady use

without such a support. The mota layer is generally found throughout the indo-Gangtic plain.


erent thicknesses and depths at different places.


siderably increase its yield. Depending upon the availability of such a provision,

Shallow wells are those which rest in a pervious stratum and draw their suppliers from



. 4016. The term “Mota layer”



not applied to layers of hard material lying above



a heavy masonry well which would not remain stable under steady use

Gangtic plain.


The nomenclature of shallow and deep wells is purely technical and has nothing to do

with the actual depth of the well. A “shallow well” might be having more depth than a “deep

well”.

Since a shallow well draws water from the topmost water bearing stratum, its water is

liable to be contaminated by the rain water percolating in the vicinity and may take with it

minerals or organic matters such as decomposing animals and plants, etc. The water in a deep

well, on the other hand, is not liable to get such impurities and infections. Secondly, the

pervious formations below the mota layer generally contain greater discharge and greater

supplies can be obtained from a deep well as compared to those from a shallow wel

Water is generally drawn from dug or open wells by means of a bucket and a rope.

However, due to the possible surface contamination of water in an uncovered well and also

the individual buckets adding contamination to water, such open wells have been co

many parts of India and fitted with hand pumps (Fig. 4" 15).

2.1 Cavity Formation in Wells.

withdrawn. The water level in such a well will obviously be the same as is the static

watertable outside the well. Now, if a discharge is withdrawn from this well at a constant

rate, the level in the well will go down and stabilise at a lower level than that of the outside

watertable. The head difference between these two levels is called depression head (Fig.

4.17). Under the influence of this head difference, water enters the well from outside so as to

fill

the gap created by withdrawn water. As the water from the surrounding soil travels towards

the well, there is a gradual loss of head, and water surf

same discharge is passing through reducing soil areas as it approaches the well, there is a

gradual increase in flow velocity towards the well. Now according to Darcy's law, this

velocity can gradually increase only if

the water surface will fall gently in the beginning and will fall more and more rapidly as it

78



raws water from the topmost water bearing stratum, its water is



on the other hand, is not liable to get such impurities and infections. Secondly, the


supplies can be obtained from a deep well as compared to those from a shallow wel



the individual buckets adding contamination to water, such open wells have been co

many parts of India and fitted with hand pumps (Fig. 4" 15).

Cavity Formation in Wells. Consider a well from which no water is being


e well. Now, if a discharge is withdrawn from this well at a constant





the well, there is a gradual loss of head, and water surface drops towards the well. Since the



velocity can gradually increase only if the hydraulic gradient gets gradually increased. Hence,




raws water from the topmost water bearing stratum, its water is



on the other hand, is not liable to get such impurities and infections. Secondly, the


supplies can be obtained from a deep well as compared to those from a shallow well.



the individual buckets adding contamination to water, such open wells have been covered in

Consider a well from which no water is being


e well. Now, if a discharge is withdrawn from this well at a constant





ace drops towards the well. Since the



the hydraulic gradient gets gradually increased. Hence,


79

approaches the well. The surface of water-table surrounding the well, therefore, takes up a

curved shape and is called Cone of Depression. At a certain distance from the well, there is

no appreciable depression of watertable. This distance from, the central line of the well is

called radius of influence of the well.

The velocity of percolating water into the well depends upon the depression head. If

more amount of water is withdrawn from the well and thereby increasing the depression

head, higher flow velocities will prevail in the vicinity of the well. Thus, at a certain rate of

withdrawal, it is very much possible that the flow velocity may exceed the critical velocity

for the soil, thereby causing the soil particles to lift up. As more and more sand particles are

lifted, a hollow is created in the bottom of the well, resulting in increased effective area, so

that ultimately, the velocity falls below the critical value and then no further sand goes out of

the well.

As pointed out earlier, the formation of such hollows beneath the wells is dangerous

in shallow wells, because there is always a danger of subsidence of the well lining. The

maximum rate of withdrawal from such wells is, therefore, limited.

In case of deep well resting on mota layer, the cavity or hollow formation below the

bore hole (Fig. 4'16) is not dangerous, because the well lining remains supported on the mota

layer. Hence, a hollow, much larger in area than the cross-sectional area of the well, may

safely form in deep wells, and thereby giving higher yields. In a shallow well of an equivalent

yield, the well area will have to be increased equal to the area of the cavity under the deep

well, which would make it costlier.

2.2 Construction of Open Wells. From the construction point of view, the open wells

may be classified into the following three types :

Type I. Wells with an impervious lining, such as masonry lining, and generally resting on a

mota layer.

Type II. Wells with a pervious lining, such as dry brick or stone lining, and fed through the

pores in the lining.

Type III. No lining at all, i.e., a Kachha well.

Type I. Wells with impervious lining. They provide the most stable and useful type of wells

for obtaining water supplies. For constructing such a well, a pit is first of all excavated,

generally by hand tools, up to the soft moist soil. Masonry lining is then built up on a kerb

upto a few metres above the ground level. A "kerb" is a circular ring of R.C.C., timber or

steel having a cutting edge at the bottom and a flat top, wide enough to support the thickness

80

of well lining called "steining". The kerb is then descended into the pit by loading the

masonry by sand bags, etc. As excavation proceeds below the kerb, the masonry sinks down.

As the masonry sinks down, it is further built up at top. To ensure vertical sinking, plum bobs

are suspended around the well steinning, and if the well starts tilting, it may be corrected by

adjusting the loads or by removing the soil from below the kerb which may be causing the

tilt. The well lining (steinning) is generally reinforced with vertical steel bars.

After the well has gone up to the watertable, further excavation and sinking may be

done either by continuously removing the water through pumps, etc., or the excavation may

be carried out from top by Jhams. A Jham is a self-closing bucket which is tied to a rope and

worked up and down over a pulley. When the Jham is thrown into the well, its jaws strike the

bottom of the well, dislodging some of the soil materials. As the Jham is pulled up, the soil

cuttings get retained but the water oozes out. The sinking is continued till the mota layer is

reached. A smaller diameter bore hole is then made through the mota layer in the centre of

the well, which is generally protected by a timber lining.

Sometimes, when mota layer is not available, shallow wells may be sunk as described

above upto a required depth, and partly filled with gravel or broken ballast. This will function

as a niter through which water will percolate and enter the well but the sand particles will be

prevented from rising up.

In a pucca well, lined with an impervious lining on its sides, the flow is not radial.

The water enters only from the bottom and the flow becomes spherical when once the cavity

has been formed at the bottom.

Type II. Wells with pervious lining. In this type of wells, dry brick or stone lining is used on

the sides of the well. No mortar or binding material is used. The water, thus enters from the

sides, through the pores in the lining. The flow is, therefore, radial. Such wells are generally

plugged at the bottom by means of concrete. If the bottom is not plugged, the flow pattern

will be a combination of radial flow and a spherical flow. Such wells are generally suitable in

strata as of gravel or coarse sand. The pervious lining may have to be sorrounded by gravel,

etc., when such a well is constructed in finer soils, so as to prevent the entry of sand into the

well along with the seeping water.

Type III. Kachha wells. These are temporary wells of very-shallow depths, and are generally

constructed by cultivators for irrigation supplies in their fields. Such wells can be constructed

in hard soils, where the well walls can stand vertically without any support. They can,

therefore, be constructed only where the water-table is very near to the ground. Though they

81

are very cheap and useful, yet they collapse after some time, and may sometimes prove to be

dangerous.

2.3 Yield of an Open Well. The yield of an open well can be determined with the help

of theoretical methods, with practical methods, or by carrying out a practical test and then

calculating it from the observations. This third method is useful for calculating the yields of

open wells as well as that of tube-wells penetrating through confined aquifers.

(1) Theoretical method. If a well is penetrated through the aquifer, water will rush into it

with a velocity V. If A is the area of the aquifer opening into the well, then

Q=AV

where V=vK, where v is the actual flow velocity and V is the velocity with which water

rushes into the well and is constant.

Q=K.A.v

where K is a constant depending upon the soil and is known as permeability constant.

In the above equation, the velocity of ground water flow (v) can be found by using Slichter's

or Hazen's formula or by actual measurements by chemical or electrical methods.

A, the area of the aquifer, and can be found by knowing the •diameter of the well and

the depth of porous strata.

K, the constant can be found by studying the sample of the soil in the laboratory.

Knowing v, A and K, the discharge can be easily calculated.

2.3 Tube-wells.

The discharge from an open well is generally limited to 3 to 6 litres/sec. Mechanical

pumping of small discharges available in open wells is not econofnical. To obtain large

discharge mechanically, tubewell, which is a long pipe or a tube, is bored or drilled deep into

the ground, intercepting one or more water bearing stratum. The discharge of an open well is

smaller, because : (0 open wells can tap only the topmost or at the most the next lower water

bearing stratum. O'O water from open wells can be withdrawn only at velocity equal to or

smaller than the critical velocity for the soil, so as to avoid the danger of well subsidence. But

in the tube wells, larger discharges can be obtained by getting a larger velocity as well as a

larger cross-sectional area of the water bearing stratum. Since, we have an enormous storage

of ground water in India, the tubewells provide excellent means for providing water supplies,

although they are generally used for irrigation.

2.4 Tube-Wells in Alluvial Soil. Most of our land, especially the entire area from

Himalayas to Vindhya mountains (such as the Indo-Gangetic plain), coastal areas, Narmada

valley, etc., consist of deep alluvial soils. The subsoil water slowly penetrates and is stored in

82

the porous sand and gravel beds which are extensively found in India, except that in the

desert areas. Tube-wells can be easily installed in such soils and are very useful for irrigation.

It is in this context that the tube-wells are assuming greater and greater importance for

tapping out ground water resources, especially in alluviums.

Deep tube-wells are generally constructed by Government and are called State tube-

wells The depth of such wells, generally vary from 50 to 500 m, and may yield as high as 200

litres/sec. The general average yield from the standard tube-wells is of the order of 40 to 45

litr. s/sec. A 300 m deep tube-well has been constructed at Allahabad (UP.) at the edge of

river Gauges, and is yielding at about 140 litres/sec. Trie diameter of the hole is 0"6 m upto

60 m depth, and then 0'56 m below 60 m. The diameter of the strainer is 0'25 m, and

drawdown is 10 m. Tnere are about 20,000 ■deep tube wells in our country, and every year

about 1,500 such wells are being added.

Besides deep tube-wells, shallow tube-wells are also constructed by cultivators. Their

depths generally vary from 20 to 40 m or so, and may yield as high as 15 litres/sec, if located

at proper places. Each well iirigates about 8 hectares. There are about 10 lakh shallow tube-

wells in India, and every year about 1'5 lakh such wells are being added

2.5 Tube-wells in Hard Rocky Soils. It is very difficult to construct a tube-well

irrigation system in rocky areas. Therefore, in rocky areas, tube-wells or open wells are

resorted to, only when, there are no other alternate sources of water. Hence, in rocky areas,

only isolated holes of 10 to 15 cm diameter may sometimes be drilled using down the hole

rigs. Only wells in alluviums have been treated here.

2.6 Various Types of Tube-wells. Tube-wells are generally of the following types :

(1) Strainer wells ;

(2) Cavity wells ;

(3) Slotted wells ; and

(4) Perforated pipe wells.

Out of these four types, the first type, i.e., the strainer wells •are the most important

and widely used in India, while the last type, i.e., perforated pipe wells are not of much

importance, as they have not been used in India to any appreciable extent. The first three

important types of tube-wells are described below :

(1) Strainer Type Tube-wells. As pointed out earlier, a strainer well is the most

important of all the types of tube-wells, and has been extensively and widely used in our

country. So much so that whenever we refer to a 'tube-well', we generally mean a strainer

type of a'iube-well'. All the state tube

tube-well construction got started in 1931, are exclusively of this type.

In this type of a well, a strainer or a screen is placed against the water bearing stratum.

The strainer is generally constructed of a wire screen wrapped round a slotted or perforat

pipe with a small annular space between the two. The wire screen prevents sand particles

from entering the tube-well. The water, therefore, enters the well pipe through the fine mesh

(i.e., the screen) and the sand particles of size larger than the si

from entering the pipe. This reduces the danger of sand removal and hence, larger flow

velocities can be permitted. Moreover, the strainer penetrates into a number of water bearing

strata, and thus* does not depend only on one

pipe is made to have the cross-sectional area of its openings equal to that in the wire screen,

so that no change of velocity occurs between the two. The annular space between the pipe

and the screen is required, otherwise the wires of the screen part of the of the opening of the

pipe.

The strainer type of tube

because in that case, the size of the screen opening will have to be considerably reduced,

which may result in chocking of the strainer, and if the screen openings are kept bigger, the

well will start discharging sand.

The boring for such a well is generally carried out by a "casing pipe of about 5 to 10

cm larger than the diameter of the well pipe. Thus, for a 15 cm diameter well, a bore hole of

20 to 25 cm diameter shall be drilled. After boring the hole, the well pipe assembly which is

partly in ordinary plain pipe (called blind pipe) and partly of strainer pipe, is lowered into th

83

well'. All the state tube-wells constructed in U.P., from where the technique of

well construction got started in 1931, are exclusively of this type.


The strainer is generally constructed of a wire screen wrapped round a slotted or perforat


well. The water, therefore, enters the well pipe through the fine mesh

(i.e., the screen) and the sand particles of size larger than the size of the mesh, are kept away



strata, and thus* does not depend only on one or two strata for the well supplies. The slotted

sectional area of its openings equal to that in the wire screen,


uired, otherwise the wires of the screen part of the of the opening of the

The strainer type of tube-well is generally unsuitable for very fine sandy strata,




f the well pipe. Thus, for a 15 cm diameter well, a bore hole of


partly in ordinary plain pipe (called blind pipe) and partly of strainer pipe, is lowered into th

wells constructed in U.P., from where the technique of


The strainer is generally constructed of a wire screen wrapped round a slotted or perforated


well. The water, therefore, enters the well pipe through the fine mesh

ze of the mesh, are kept away



or two strata for the well supplies. The slotted

sectional area of its openings equal to that in the wire screen,


uired, otherwise the wires of the screen part of the of the opening of the

well is generally unsuitable for very fine sandy strata,




f the well pipe. Thus, for a 15 cm diameter well, a bore hole of


partly in ordinary plain pipe (called blind pipe) and partly of strainer pipe, is lowered into the

bore hole. The lengths of blind pipe and strainer pipe are so adjusted that the blind pipe rests

against the aquicludes, while the strainer rests against the aquifers, as shown in Fig 4'19. At

bottom, a short blind pipe is provided, so as to permit settl

passed through the strainer. The well is generally plugged at bottom by cement concrete.

Abyssinia tube-well is a special type of strainer well, in which the diameter of the well pipe is

kept equal to 3'8 cm (l^T) and the st

(i.e., 4 to 5 feet).

(2) Cavity Type Tube-wells.

their supplies from the bottom, and not from the sides. Since the water is drawn from the

bottom, only one particular aquifer can be tapped. Thus, the principle behind a cavity

tube-well is essentially similar to that of a deep open well, with the only difference that

whereas an open deep well taps the first aquifer, just below the mota layer,

need not do SO;, and may even tap the lower stratum, as shown in Fig. 4'20.

A cavity type tube-well essentially consists of a pipe bored through the soil and

resting on the bottom of a strong clay layer. A cavity is for

from the aquifer enters the well pipe through this cavity, as shown in Fig. 4'20. In the initial

stages of pumping, fine sand comes out with water, and consequently, a hollow or a cavity is

formed. As the spherical area of t

84



bottom, a short blind pipe is provided, so as to permit settlement of any sand particles, if


well is a special type of strainer well, in which the diameter of the well pipe is

kept equal to 3'8 cm (l^T) and the strainer is provided only for a length of about 1.2 to l.5m

wells. They are those which do not utilise strainers and draw


om, only one particular aquifer can be tapped. Thus, the principle behind a cavity

well is essentially similar to that of a deep open well, with the only difference that

whereas an open deep well taps the first aquifer, just below the mota layer, a cavity tube

need not do SO;, and may even tap the lower stratum, as shown in Fig. 4'20.

well essentially consists of a pipe bored through the soil and

resting on the bottom of a strong clay layer. A cavity is formed at the bottom and the water



formed. As the spherical area of the cavity increases outwards, the radial critical velocity



ement of any sand particles, if


well is a special type of strainer well, in which the diameter of the well pipe is

rainer is provided only for a length of about 1.2 to l.5m

They are those which do not utilise strainers and draw


om, only one particular aquifer can be tapped. Thus, the principle behind a cavity-type

well is essentially similar to that of a deep open well, with the only difference that

a cavity tube-well

well essentially consists of a pipe bored through the soil and

med at the bottom and the water



he cavity increases outwards, the radial critical velocity

decreases for the same discharge, thus redut Yg the flow velocity and consequently stopping

the entry of sand. Hence, the flow in the beginning is sandy, but becomes clear with the

passage of time.

The essential difference in the flow pattern of a strainer well and a cavity well is that

whereas in a strainer well, the flow is radial, the flow in a cavity well is spherical. Also, in a

strainer well, the area of flow is increased by increasing the l

cavity well, the area of flow is increased by enlarging the size of the cavity. The cavity

formed with a certain discharge enlarges in size if an increased discharge is pumped out.

(3) Slotted Type Tube

available even at deep depths of 75 to 100 m, so as to obtain the required discharge from a

strainer well, and if a suitable strong clay roof is not available for a cavity well, a slotted well

is adopted, provided at least one good stratum having sufficient amount of water is available.

A slotted well essentially consists of a slotted wrought iron pipe, penetrating a highly

pervious confined aquifer (Fig. 4.21). The size of slots may be 25 mmX3mmatl0 to 12 mm

spacing. In order to prevent the entry of fine sand

particles into the pipe, the pipe is surrounded by a mixture of gravel and bajri. This mixture is

called shrouding and is poured from the top into the annular space between the strainer and

85





strainer well, the area of flow is increased by increasing the length of strainer pipe, while in a



(3) Slotted Type Tube-wells. If sufficient depth of water bearing strata is not



t least one good stratum having sufficient amount of water is available.



. In order to prevent the entry of fine sand







ength of strainer pipe, while in a



ent depth of water bearing strata is not



t least one good stratum having sufficient amount of water is available.





86

the casing pipe before withdrawing the casing pipe. The tube-well is developed by pumping

water with an air compressor or with a bigger capacity pumping set. In the process of

developing such a tube-well, water is drawn at a high rate, causing high flow velocities and

consequent removal of appreciable quantities of fine sand. Shrouding is continuously fed

through the annular space, so as to fill up the space of removed sand particles. The process is

continued till the sand-free water is obtained.

The diameter of the bore hole or casing pipe is generally kept more than that of a

strainer type of tube-well. For example, a casing pipe of about 40 cm diameter is required for

a well pipe of 15 cm diameter.

The essential difference between a strainer well and a slotted well are :

(i) A strainer well uses a 'strainer' for preventing sand entry in the water, whereas a

slotted well uses a gravel 'shrouding' for this purpose.

(ii) A strainer well can tap one or more strata, whereas a slotted well can tap only one

stratum.

2.6 Methods for Drilling Tube-wells. Deep and high capacity wells are constructed by

drilling. Various different techniques are employed in drilling the well hole. Different

techniques have comparative advantages and disadvantages over each other, depending upon

the type of formation to be drilled. Therefore, each well should be treated as an individual

project, and one particular method adopted, depending upon its suitability. Some of the

drilling methods, common'y used, are described below:

(I) Standard method or Cable tool method. This method of drilling the well hole is also

known as percussion drilling ; because in this method, the well hole is made by percussion,

(i.e., by hammering and cutting). This method is very useful for cutting consolidated rocks

from soft clay to hardest rocks, and is generally unsuitable in loose formations, such as

unconsolidated sand and gravel or for quick sands. This method becomes ineffective in loose

materials, because the loose material slumps and caves around the drilling bit. The drill bit

has a chisel sharp edge, which breaks the rocks by impact when alternately lifted and-

dropped. This drilling bit is connected at the lowest end of the entire’ falling and rising

arrangement' known as String of tools. [Refer Figs. 4'2 (a) and (b)]. From top to bottom, the

string of tools consists of a rope socket, a set of jars, a drill stem, and the drilling bit.

Tools are made of steel and are joined with tapered box and pin screw joints. The

entire assembly weighs several tonnes. The most important tool of the entire assembly is the

drilling bit (or drill) as it does the actual rock cutting. The drill stem is the long steel bar

which adds weight and length to the drill, so that it can cut rapidly and vertically.

The set of jars have no dir

they stick in the hole. A rope or a cable is fastened at the upper end to the rope socket and to

a dead man (or a heavy weight) at the lower end.

The entire assembly of tools is suspended from an

beam, etc. This assembly, known as drilling rig, in turn, is generally mointed on a truck, so as

to make it easily portable. The mast should be sufficiently high, so as to allow the longest of

tools to be hoisted.

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The set of jars have no direct effect on the drilling. They only loosen the tools when


a dead man (or a heavy weight) at the lower end.

The entire assembly of tools is suspended from an assembly of a mast and a walking



ect effect on the drilling. They only loosen the tools when


assembly of a mast and a walking



As the drilling proceeds, the tools make 40 to 60 strokes per minute, from a height of 0'4 to 1

m. Water is sometimes added in the hole, so as to form a paste with the cuttings, thus

reducing friction on the falling bit. After the bit has cut 1 to 2 m through a formation, the

string of tools is lifted out, and the hole is cleaned and cleared of the cuttings by means of a

bailer. The process is known as bailing out the hole.

A bailer essentially consists o

When lowered into the well, the valve permits the cuttings to enter the bailer but prevents

them from escaping the bailer. After it is filled with cuttings, it is lifted up to the surface and

emptied.

In unconsolidated formations, casing should be driven down and maintained near the

bottom of the hole to avoid caving. Casing is driven down by means of drive clamps fastened

to the drill stem. The up and down motion of the tools, striking the top of

protected by a drive head, sinks the casing. On the bottom of the casing, a drive shoe is

fastened to protect the casing, as it is being driven.

(2) Hydraulic rotary or Direct rotary method.

and is especially useful in unconsolidated formations. The method involves a continuously

rotating hollow bit, through which a mixture of clay and water or mud is forced. The bit

cuttings are carried up in the hole by the rising mud. No casing is required during drilli

because the mud itself makes a lining on the walls of the hole, which prevents caving.

The drill bit is connected to a hollow steel rod (or drill stem), which, in turn, is

connected at the top to a square rod, known as the Kelley [Refer Fig. 4'23 (a)].

rotated by a rotating

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the falling bit. After the bit has cut 1 to 2 m through a formation, the


bailer. The process is known as bailing out the hole.

A bailer essentially consists of a pipe with a valve at the bottom and a ring at the top.





to the drill stem. The up and down motion of the tools, striking the top of


fastened to protect the casing, as it is being driven.

Hydraulic rotary or Direct rotary method. This is the fastest method of drilling,

ally useful in unconsolidated formations. The method involves a continuously


cuttings are carried up in the hole by the rising mud. No casing is required during drilli



connected at the top to a square rod, known as the Kelley [Refer Fig. 4'23 (a)].



the falling bit. After the bit has cut 1 to 2 m through a formation, the


f a pipe with a valve at the bottom and a ring at the top.





to the drill stem. The up and down motion of the tools, striking the top of the casing,


This is the fastest method of drilling,

ally useful in unconsolidated formations. The method involves a continuously


cuttings are carried up in the hole by the rising mud. No casing is required during drilling,



connected at the top to a square rod, known as the Kelley [Refer Fig. 4'23 (a)]. The drill is

table which fits closely around the Kelley, and allows the drill rod to slide down, as the hole

progresses.

The drilling rig, such as shown Fig. 4'23 (b), consists of a mast, a rotating table, a

pump for forcing the mud, a hoist and the engine. The mud, after it emerges out of the hole, is

carried to & tank where the cuttings settle out, and the mud can be repumped into the hole.

After the drilling is completed, the casing is lowered into t

in the well-walls during mud pumping, is removed by washing it with water. Water

containing some chemicals like sodium hexametaphosphate is forced through the drill rod,

and the washings come out through the perforations of the

level is completed, the bit is raised and the process repeated.

(3) Reverse Rotary method or Jetting method

method is known as Reverse Rotary method. This is gaining popularity day by

useful for making large wells (diameter up to 1'2 m. app.) in unconsolidated formations.

This method is also known as jetting method. The tool consists of a hollow drill, a drill pipe,

and water swivel. In this method, the cuttings are

called drill pipe. The equipment consists of a mast or a derrick, a centrifugal pump, and

necessary water and power casing.

90



ing the mud, a hoist and the engine. The mud, after it emerges out of the hole, is


After the drilling is completed, the casing is lowered into the hole. The clay, deposited

walls during mud pumping, is removed by washing it with water. Water


and the washings come out through the perforations of the casing When the washing at one

level is completed, the bit is raised and the process repeated.

Reverse Rotary method or Jetting method. A modification of the hydraulic rotary

method is known as Reverse Rotary method. This is gaining popularity day by day. It is quite



and water swivel. In this method, the cuttings are removed by water through a suction pipe


necessary water and power casing.



ing the mud, a hoist and the engine. The mud, after it emerges out of the hole, is


he hole. The clay, deposited

walls during mud pumping, is removed by washing it with water. Water


casing When the washing at one

. A modification of the hydraulic rotary

day. It is quite



removed by water through a suction pipe


The hole is driven by pumping water under pressure through

churned up and down.

The walls of the hole are supported by hydrostatic pressure acting against a film of

fine grained material deposited on the walls by the drilling water. Cuttings are removed by

water ; and after the mixture (water + cuttings) comes out to the surface, it is passed through

a settling tank (Refer Fig. 4'24).

The sand settles out here, but the fine grained particles are recalculated, so as to help

in stabilising the walls. Casing and cleaning of the walls, etc. i

rotary method.

91

The hole is driven by pumping water under pressure through the drill bit, while it is



water + cuttings) comes out to the surface, it is passed through


in stabilising the walls. Casing and cleaning of the walls, etc. is the same as in the hydraulic

the drill bit, while it is



water + cuttings) comes out to the surface, it is passed through


s the same as in the hydraulic

92

Comparison of Cable Tool and Hydraulic Rotary methods.

Advantages of Cable Tool Method are given below :

1. A more accurate sample of the formation can be obtained.

2. Lesser amount of water is required during drilling operations.

3. Cable tool rig is lighter and easy to transport.

4. Very useful for consolidated rocks and less useful for loose formations.

5. For shallow-wells, in unconsolidated materials too, it comes out to be cheaper.

Advantages of Hydraulic Rotary Method are given below :

1. Can be used for larger holes up to 1'5 m diameter.

2. Can be best used for drilling test holes, because the hole can be abandoned with

minimum cost.

3. Rotary drilled hole can be gravel packed, which increases its specific capacity, and

keeps the fine particles away, thus causing less sand trouble.

4. Casing is to be driven only after the hole completion, and hence, can be set at any

desired depth.

5. It is the fastest method of drilling and especially useful in unconsolidated formations.

6. It can handle alternate hard and soft formations with ease and the danger of accidents

is lesser. In quick sands, clays, etc., cable tool method is likely to give troubles, as

there is a danger of freezing.

2.7 Completion of a Tube-well. During drilling the well hole by any of the above

methods, care should be taken to see that the hole remains straight and vertical. A common

specification allows a deviation of 15 cm from the vertical in a length of 30 m. After the bore

hole has been constructed or drilled, the well must be completed, so as to provide free

entrance of clear water into the well.

Casings and Screens. In consolidated formations, water enters the well hole directly,

and no casing is provided, because the surroundings are quite stable. But in unconsolidated

formations, a casing is necessary which supports the outside material and helps in freely

admitting water into the well.

For the entry of water, the casing should either contain perforations or its lower part

be replaced by a screen or a strainer. Perforations can be made in the field or at home.

Horizontal louvered openings are generally preferred, and their size is kept between De0 to

D70 of the surrounding soil. Generally, a separate screen forms the lowest part of the casing.

They are made from various corrosion-resistant metals. Plastic screens are also forming their

way in the market. Well-screens are very useful in sandy formations, so that the water

containing only a limited quantity of sand (below a given size) may e

bigger particles are screened and kept away from entering the well. However, the mesh size

of the screen is generally decided by the manufacturer for a given project, depending upon

the grain size distribution of the aquifer.

Gravel Packing. Many a times, a layer of gravel surrounding the screen casing, is

provided, so as to increase the effective well diameter and to keep the fine materials out of

the well. Such a well will have a greater specific capacity than the one of the same d

not surrounded by gravel. The thickness of the gravel may vary with the type of formation

and method of drilling. However, a minimum of 15 cm thickness is generally used. A section

of the gravel packed well is shown in Fig. 4'25.

2.8 Factors Affecting the Selection of a Particular Type of Pump.

The various factors which must be thoroughly considered while selecting a particular

type of a pump for a particular project are:

(i) Capacity of pumps

(ii) Importance of water supply scheme

(iii) Initial cost of pumping arrangement

(iv) Maintenance cost

93

screens are very useful in sandy formations, so that the water

containing only a limited quantity of sand (below a given size) may enter the well, and the



the grain size distribution of the aquifer.

Packing. Many a times, a layer of gravel surrounding the screen casing, is


the well. Such a well will have a greater specific capacity than the one of the same d



of the gravel packed well is shown in Fig. 4'25.

Factors Affecting the Selection of a Particular Type of Pump.


type of a pump for a particular project are:

Capacity of pumps

Importance of water supply scheme

l cost of pumping arrangement

screens are very useful in sandy formations, so that the water

nter the well, and the



Packing. Many a times, a layer of gravel surrounding the screen casing, is


the well. Such a well will have a greater specific capacity than the one of the same diameter




94

(v) Space requirements for locating the pupm

(vi) Number of units required

(vii) Total lift of water required

(viii) Quantity of water to be pumped

Truly speaking, reciprocating pumps are also outdated these days, and for all ordinary

conditions of pumping, the centrifugal types of rot dynamic pumps are frequently used these

days, as they provide satisfactory and economic service. However, pumps other than those of

centrifugal types may be used under extreme conditions. The choice between various types of

pumps is guided by the following considerations:

For very small discharge, the rotary pumps may prove to be equally satisfactory as the

centrifugal pumps, and less costly if the water to be pumped is free of sediment.

A centrifugal pump may pose operational problems when constant discharge is

needed at variable heads (because it requires a variable speed driving in that case) whereas,

the discharge through a reciprocating pump depends only on the speed of the pump. Hence,

under such circumstances, where water is to be pumped against very high but variable heads

with a higher suction lift, reciprocating pumps may be useful. However, they can be used

only when the water to be pumped is free of sediment, and ample finances are available for

installing the costly reciprocating pumps.

Centrifugal pumps are especially useful for pumping waste water and water

containing solids, although they are equally suitable for pumping treated waters. Even among

the centrifugal pumps, a choice is sometimes made out of the horizontal shaft centrifugal

pump and the vertical spindle bore hole pump and the submergible pump. The horizontal

pump is the cheapest and is used under a wide range of pumping conditions, but vertical

spindle and submergible pumps may be preferred for handling large quantities of water under

low heads and for wells and bore holes.

Air lift pumps may prove to be cheaper and, therefore, selected when water is

required to be pumped simultaneously from a number of wells; because in that case, a

common compressor unit can be used to feed all the pumps. However, their efficiency is

generally low.

The hydraulic ram and jet pumps may also be used under special circumstances, as

pointed out earlier.

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